THE  EFFICIENCY  OF  PUMPS 
AND  EJECTOKS 


THE   EFFICIENCY   OF 
PUMPS  AND  EJECTORS 


BY 


E.  C.  BOWDEN-SMITH,  M.I.MECH.E. 

•'> 

LATE    EGYPTIAN   CIVIL    SERVICE 

AUTHOR  OF 

'OIL   FIRING   FOR    KITCHEN  RANGES  AND   STEAM  BOILERS,' 

'THE  SUBSOIL  OF  CAIRO,'    'INVENTION,   AN   ELEMENTARY  ANALYSIS,' 

'THE  GREATKST   POSSIBLE   POWER   FOR  THE   LEAST  POSSIBLE   WEIGHT,'  ETC. 


•*•       •»       »        „•,«.,•      •         *3 


NEW  YORK 
D.  VAN  NOSTRAND  COMPANY 

EIGHT  WARREN  STREET 
1920 


Engineering 
Library 


1» 


Printed  in  Great  Britain 


FOREWORD 

E/ANKINE  defined  efficiency  as  the  ratio  of  useful  work  to 
energy  expended.  No  doubt  he  was  particularly  refer- 
ring to  the  heat  engine  ;  but  if  we  substitute  £.  s.  d.  for 
energy — that  is,  the  cost  of  conversion  and  application — 
the  definition  is  equally  applicable  to  the  subject  under 
discussion.  After  all,  the  mechanical  efficiency  is  simply 
the  relative  value  of  one  power  engine  to  that  of  another. 
The  term  is  one  of  comparison,  in  whatever  respect  it 
is  utilised.  To  regard  with  discriminating  attention 
the  means  employed  to  perform  a  certain  task  is  essential 
to  progress,  and  the  surest  method  of  disposing  of  mis- 
conception and  prejudice. 

The  object  now  in  view  is  to  throw  some  additional 
light  on  the  most  efficient  method  of  raising  crude  sewage. 
What  is  well  known  will  not  be  amplified,  what  is 
obscure  will  be  analysed,  and  that  which  is  open  to 
question  substantiated,  with  records  and  precise  informa- 
tion as  to  how  they  were  obtained. 

At  the  same  time,  chapters  have  been  given  on  the 
sinking  of  Ejector  Tubbings,  faults  and  remedies  in 
the  erection  and  working  of  Ejector  Systems,  and  sug- 
gestions as  to  how  the  efficiency  may  be  improved. 
There  has  been  no  attempt  to  cover  the  whole  ground, 
but  to  enumerate  and  discuss  those  points  which  tend 
to  the  economical  raising  of  crude  sewage,  which  are 
not  to  be  found  in  the  engineers'  handbooks  on  city 
drainage. 

A  mere  statement  of  original  data  on  which  results 

a2 

48I5U5 


vi     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

are  based  is  neither  convincing  nor  satisfactory,  as  the 
basis  of  calculation  must  be  above  contention.  The 
efficiency  of  the  motive  power  has  been  repeatedly 
determined,  but  the  efficiency  of  the  mechanical  apparatus 
that  does  the  work  is  often  a  matter  of  controversy. 
Especially  is  this  the  case  in  drawing  comparisons  between 
pumps  and  ejectors.  The  pump  maker  recommends 
his  pump  as  the  most  efficient  engine.  The  ejector  maker 
recommends  his  ejector  as  the  most  efficient  engine.  And 
the  purchaser,  in  nine  cases  out  of  ten,  is  left  to  decide 
on  mechanical  efficiencies  obtained  at  a  prearranged 
trial,  and  second-hand  contradictory  evidence  applic- 
able to  those  conditions  of  locality  from  which  the 

information  is  derived. 

E.  C.  B.-S. 

LONDON,  January  1920. 


CONTENTS 

CHAPTER  I 

EFFICIENCIES  AND  RECIPROCATING  PUMPS 

PAOX 

Efficiency  defined — Mechanical  efficiency  —  Commercial  effi- 
ciency—  Sanitary  efficiency — Raising  sewage:  various 
methods  —  Crude  sewage  defined  —  Pumps'  analysis  — 
Water :  behaviour  in  motion  and  under  pressure — Pumps : 
reciprocating — Pump  suction — Suction  wells — Air  in  pumps 
— Matter  in  pumps — Strainer  for  suction  pipe — Foot  valves 
— Air  vessels — Pump  valves — Multiple  clear-way  valves  .  1 

CHAPTER  II 

CENTRIFUGAL  PUMPS   AND   EJECTORS 

Centrifugal  pumps — Centrifugal  pumps  with  vertical  shafts — 
Pneumatic  ejectors  in  tubbings — Subsidiary  ejectors — De- 
scription of  ejectors — Action  of  ejectors  on  sewage  — 
Localities  classified  —  Machinery:  suitable  conditions — 
Sectional  systems :  alternatives  —  Hydraulic  system  — 
Centrifugal  pumps:  multiple  system  —  Sumps:  dangers 
from  gas  —  Sumps:  dangers  from  explosion  —  Electric 
motors — Motors'  reliability — Refuse  in  sewage  .  *.  24 

CHAPTER  III 

MECHANICAL  EFFICIENCY  OF  PUMPS  AND  EJECTORS 

Mechanical  efficiency — Efficiency  diagram — Calibrating  dis- 
charge— Ejectors:  capacity  and  discharge — Calibrating 
ejectors — Discharge  table — Calibrating  ejectors  by  measure- 
ment— Calibrating  ejectors  by  weight  of  water  expelled — 
Ejector  discharge  compared  with  Venturi  meter — Chemical 
test  of  Venturi  meter — Pressure-gauge  errors — Air  mains : 
proportional  loss — Air-main  testing — Ejector  trials:  con- 
ditions— Ejector  efficiency  diagram — Ejector  efficiency  trials 
— Ejector  trial:  remarks — Ejector  and  pump  trials  com- 
pared— Reciprocating  pump  trial — Summary  of  efficiencies  43 

vii 


vui     EFFICIENCY  OF  PUMPS  AND  EJECTORS 
CHAPTER  IV 

COMMERCIAL   EFFICIENCY 

PAGE 

Pumping  installation :  summary — Sump — Screening  chamber — 
Auxiliaries — Rising  main — Working  of  pump  station — 
Pumping  installations:  advantages  and  merits — Ejector 
installations:  summary — Ejector  stations — Air  mains — 
Sealed  sewage  mains — Working  of  ejector  system :  com- 
pressing air  —  Ejector  installations:  advantages  and 
merits — Capital  cost — Maintenance — Reports — Daily  dis- 
charge— Maintenance  tables :  pumps — Maintenance  costs  of 
reciprocating  and  centrifugal  pumps — Maintenance  tables : 
ejectors  —  Maintenance  costs  of  ejector  system  —  Main- 
tenance :  difficulties  of  comparison — Commercial  efficiency : 
table  of  pumps  and  ejectors  .  '  '..  .  .  .  .  .  65 

CHAPTER  V 
STAFF:  SUPERVISING 

Pumping  -  station  staff  —  Ejector -system  staff  —  Ejector -in- 
spectors' duties — Quarters  for  staff — Inspection  of  ejectors 
— Selection  of  staff  ,::.  .  «  .  .  .  .-87 

CHAPTER  VI 

SINKING  AND  ERECTION  OF  CAST-IRON  TUBBINGS 

Cast-iron  tubbings — Marking  out  tubbing — Sinking  tubbing — 
Air  lock  for  sinking  tubbing — Sinking  under  pressure — 
Tubbing  floor:  fixing  in  place — Setting  ejectors  in  position 
— Ejector  inlet  pipe — Tubbing  sinking  by  pump  or  grab — 
Brick  chambers — Testing  tubbings  and  brick  chambers — 
Air,  compressed,  for  sinking  tubbings  .  »  •  *  100 

CHAPTER  VII 

EJECTOR  AND  AIR-MAIN  FAULTS  AND  REMEDIES 

Causes  of  ejectors  stopping — Silencing  chamber  for  exhaust — 
Blow  through — Sand  and  stones  in  ejectors — Choking  of 
ejectors — Floating  matter — Leakage  through  slide- valve 
box — Examination  of  ejector  valves — Stopping  ejectors — 


CONTENTS  ix 

PAOK 

False  discharges  —  Ventilation  of  tubbing  —  Painting 
machinery — Entrance  covers  to  ejector  tubbings — Reflux 
valves — Air  valves  in  tubbing — Underground  obstructions 
— Disc  valves — Air  mains — Laying  air  mains — Caulking  pipe 
joints — Testing  air  mains  when  laid — Detecting  leakage — 
Filling  trenches  and  rammers — Water  in  air  mains — Air  stop 
valves — Valve  chambers — Accidents  to  air  mains — Laying 
rising  mains — Back  pressure  in  mains — Fouling  of  mains — 
Locating  stoppage  in  mains — Air  lock  in  mains — Inspection 
openings  and  bends — Scour  valves — Bursting  of  mains — 
Indicator  plates  «  «  *  .  *  ...  •  111 

CHAPTER  VIII 

THE    SANITARY   EFFICIENCY 

Gravitation  scheme  —  The  subsoil  —  Conditions  for  sanitary 
efficiency — Sectional  system — Grade  of  sewers — Reasons 
of  preference  for  small  pumps — Typical  example  of  small 
sewerage  scheme  .  .  ..,  .  •  .  .  f  .  •  133 

CHAPTER  IX 

POWER  HOUSE 

Power  house — Power  engines  compared — Power-house  design — 
Foundations  for  machinery — Ventilation — Engine-house 
floor — Steam  mains — Accessories — Water  supply — Air  cooler 
— Volume  of  air  to  raise  sewage — Economy  in  running 
plant — Fuel — Oil  firing  water-tube  boilers — Gas  firing  .  147 

CHAPTER  X 

IMPROVEMENTS 

Reasons  for  inefficiency — Improvements  suggested — Compressed 
air :  latent  power — Compounding  ejectors — Exhaust :  waste 
of  power — Objections  to  compounding  ejectors — Recom- 
pressing  the  exhaust — Expansion  of  air  in  the  ejector — The 
loss  from  air  mains — Electric  transmission — Selling  com- 
pressed air — Uses  of  compressed  air — Compressed  air  for 
domestic  oil  firing — Cost  of  compressing  air — Consumption 
of  air  for  liquid-fuel  burners — Cost  of  oil  firing  with  com- 
pressed air — Air  storage — Reasons  of  fluctuation  in  air 
pressure :  remedies — Improvements  defined  .  .  .  174 

INDEX  203 


ILLUSTRATIONS 

PLATE  PAGB 

I.  SINGLE-ACTING  RECIPROCATING  PUMP   .  .9 

II.  LEATHER-HINGED  PUMP  VALVE             .  .        16 

III.  MULTIPLE  CLEAR-WAY  VALVE  PLATE   .  facing    16 

TV  17 

-*•  *  •                           »                           3J                           J>                       )>  JJ                   •*•  ' 

V.  CLEAR-WAY  PUMP  VALVE        .            .  .        18 

VI.  MULTIPLE  CLEAR-WAY  VALVE  PLATE  .  »        20 

VII.  NEST  OF  CLEAR-WAY  PUMP  VALVES     .  .         22 

VIII.  EJECTORS  IN  CAST-IRON  TUBBING         .  facing    26 

IX.  PNEUMATIC  EJECTORS    .            »            ,  .        28 

X.  EJECTOR  DIAGRAM        ,            .            *  .        30 

XI.  MECHANICAL  EFFICIENCY  DIAGRAM      .  .44 

XII.  EJECTOR  EFFICIENCY  DIAGRAM             .  .        58 

XIII.  VERTICAL  STEAM  PUMPING  ENGINE     .  facing    65 

XIV.  HORIZONTAL  AIR-COMPRESSING  ENGINES  „        70 

•A.V.                  ,,                     ,,                     ,,                  .  ,,           71 

XVI.  Am  STOP  VALVE          *            .            ;  .       128 

XVII.  PLAN  OF  CAIRO  UNDERGROUND  STRUCTURE     .       136 

XVIII.  GROUND  SECTIONS  OF  CAIRO    .            ,  .       138 

XIX.          „            „                           .  v      140 

XX.  AIR  TEMPERATURE  DIAGRAM    .            .  .157 

XXI.  EJECTOR  DISCHARGE  DIAGRAM  .            .  .159 

XXII.  VOLUME  OF  AIR  TO  RAISE  SEWAGE  DIAGRAM  .       161 

XXIII.  EJECTOR  DISCHARGE  DIAGRAM.            .  ,       162 

XXIV.  VOLUME  OF  AIR  TO  RAISE  SEWAGE  DIAGRAM  .       163 
XXV,  EJECTOR  DISCHARGE  DIAGRAM  .            .  .165 

XXVI.  VOLUME  OF  AIR  TO  RAISE  SEWAGE  DIAGRAM  .       167 

XXVII.  OIL-FIRING  BABCOCK  AND  WILCOX  BOILER  .       169 

XXVIII.  171 


CHAPTER  I 
EFFICIENCIES  AND  RECIPROCATING  PUMPS 

EFFICIENCY  DEFINED. 

IN  referring  to  the  efficiency  of  the  method  employed  in 
raising  a  liquid,  the  mechanical  efficiency  and  the  first 
cost  are  too  often  permitted  to  be  the  deciding  factor 
on  which  a  decision  is  made.  In  raising  crude  sewage, 
there  is  not  one  efficiency,  but  three  efficiencies  of  equal 
importance  that  must  be  considered. 
They  may  be  defined  as  follows  : 

A.  The  Mechanical  Efficiency. 

B.  The  Commercial  Efficiency. 

C.  The  Sanitary  Efficiency. 

MECHANICAL  EFFICIENCY. 

The  mechanical  efficiency  is  plainly  a  technical  term 
that  relates  to  the  proportion  of  useful  work  done  by 
the  power  employed  to  do  it.  Compared  to  '  B  '  and 
'  C  '  it  can  be  accurately  calculated  by  the  engineer  and 
manufacturer.  Guaranteed  on  a  trial,  and,  provided 
the  apparatus  retains  that  efficiency,  it  is  possible  to 
raise  a  certain  volume  of  liquid  each  year  for  a  certain 
expenditure  in  fuel. 

COMMERCIAL  EFFICIENCY. 

The  commercial  efficiency  is  the  cost  of  raising  the 
liquid.  Not  only  the  yearly  expenditure  on  maintenance 

A 


2       EFFICIENCY  OF  PUMPS  AND  EJECTORS 

in  proportion  to  the  volume  raised,  but  the  capital  cost 
of  the  installation,  the  laying  of  sewers,  purchase  of  land, 
compensation,  and  every  expense  that  can  be  reasonably 
foreseen  must  also  be  considered.  Inexpensive  machinery 
may  result  in  high  maintenance.  On  the  other  hand, 
additional  capital  expenditure  may  be  justified  by 
economy  in  working. 

SANITARY  EFFICIENCY. 

The  sanitary  efficiency  obviously  embraces  the  whole 
undertaking,  and  cannot  be  confined  to  the  machinery. 
It  is  synonymous  with  cleanliness  and  health.  In  fact, 
it  is  a  stipulation  that  neither  directly  nor  indirectly  shall 
the  effluent  to  be  raised  become  a  nuisance  to  the  public. 
Expense  on  this  head  is  an  insurance  policy  against 
disease  and  offensive  odours.  If  one  type  of  pump  or 
ejector  will  raise  the  sewage  in  a  less  offensive  manner 
than  another,  it  should  be  carefully  considered,  even 
if  the  initial  expense  is  greater. 

RAISING  SEWAGE  :  VARIOUS  METHODS. 

Exclusive  of  exceptional  situations,  where  a  natural 
fall  can  be  utilised  as  a  motive  power,  such,  for  instance, 
as  the  hydraulic -lift  system,  the  methods  of  raising 
sewage  in  common  use  are  as  follows  : 

1.  The  single-acting  Ram  Pump. 

2.  The  double-acting  Plunger  Pump. 

3.  The  Centrifugal  Pump. 

4.  The  Pneumatic  Ejector. 

They  are  representative  of  the  class  of  machinery 
usually  adopted  ;  but  it  must  not  be  assumed  they  are 
placed  in  order  of  merit,  as  that  is  a  matter  of  opinion, 
dependent  on  the  particular  work  they  have  to  do. 


EFFICIENCIES  AND  RECIPROCATING  PUMPS      3 

CRUDE  SEWAGE  DEFINED. 

Mechanically  speaking,  crude  sewage  consists  of  the 
effluent  discharged  by  city  sewers,  containing  every 
conceivable  substance  and  variety  of  refuse  that  may 
cause  obstruction  or  destruction  to  mechanical  parts. 
Storm  water  and  land  drainage  do  not  offer  the  same 
difficulties,  and  it  is  an  error  to  assume  that  a  pump 
which  is  efficient  in  one  case  will  be  equally  efficient  in 
the  other. 

PUMPS:  ANALYSIS. 

Superficially  a  fluid  pump  is  a  simple  mechanical 
apparatus.  Analytically  it  is  one  of  the  most  enig- 
matical power  problems  that  exists.  And  furthermore,  it 
may  be  stated  with  confidence  that  there  is  nothing  more 
difficult  to  lucidly  explain  and  logically  discuss  than 
the  complex  and  intricate  behaviour  of  the  forces  set 
in  motion.  Many  people,  even  engineers,  are  under  the 
impression  that  a  pump  which  will  discharge  water  con- 
tinuously and  efficiently  is  equally  suitable  for  raising 
a  drainage  effluent.  No  greater  fallacy  ever  existed. 

To  pump  water  under  the  average  city  supply  con- 
ditions the  highest  class  of  machinery  is  required  ;  but 
to  pump  drainage  an  altogether  superlative  excellence 
of  design  and  workmanship  is  necessary  if  any  measure 
of  success  is  to  be  attained.  Many  circumstances  which 
cannot  be  foreseen  have  to  be  provided  for,  that  are 
far  beyond  the  calculations  of  the  mathematician  or 
the  ingenuity  of  the  most  intelligent  draughtsman. 

The  true  sewage  pump,  it  must  be  remembered,  should 
be  able  to  raise  and  discharge  a  liquid  or  viscous  fluid 
containing  every  conceivable  substance  and  variety  of 
refuse,  which  may  cause  obstruction  or  destruction  to 
mechanical  parts. 


4      EFFICIENCY  OF  PUMPS  AND  EJECTORS 

It  is  not  proposed  to  cover  every  point  in  connection 
with  the  subject  under  discussion,  but  merely  to  lay 
stress  on  some  of  the  salient  features  and  analyse  the 
component  sections  that  go  to  make  up  the  complete 
machine. 

At  the  same  time  it  is  as  well  to  touch  on  some  of  those 
elementary  laws  which  govern  flow  and  pressure,  and 
examine  those  conditions  which  are  detrimental  to 
efficiency.  There  must  be  a  full  appreciation  of  the 
relative  value  between  the  power,  the  machine,  and  the 
work  it  is  doing. 

The  power  is  the  force  generated.  The  machine  is 
the  medium  of  transmission.  The  work  to  be  done  is 
that  to  which  the  power  is  applied.  The  object  is  to 
maintain  an  equilibrium  between  the  power  and  the 
work,  the  one  balanced  against  the  other.  The  more 
accurately  and  scientifically  this  is  accomplished,  the 
less  will  be  lost  in  the  process  of  conversion.  As  far 
as  we  are  concerned  for  the  present,  the  source  of  all 
power  is  the  heat  engine  in  one  form  or  another.  Steam 
can  be  applied  directly  to  the  work — that  is,  can  be 
brought  in  contact  with  the  water  to  be  raised — but  from 
the  nature  and  temperature  of  the  two  fluids  the  result 
is  so  wasteful  that  it  is  not  a  practical  proposition  for 
permanent  use. 

WATER  :  BEHAVIOUR  IN  MOTION  AND  UNDER  PRESSURE. 

The  text-books  tell  us  what  should  and  ought  to  happen 
when  a  moving  column  of  water  is  suddenly  checked  or 
the  inertia  of  a  fluid  has  to  be  overcome  ;  bat  the  alarm- 
ing shocks  and  amazing  pressures  that  are  at  times 
produced  are  far  beyond  what  theory  can  at  present 
account  for. 

The  action  of  free  water  is  more  or  less  understood. 


EFFICIENCIES  AND  RECIPROCATING  PUMPS      5 

For  instance,  the  pressure  due  to  an  impinging  jet  on 
a  plain  surface  is  just  twice  as  great  as  pressure  due  to 
the  head  of  water  corresponding  to  the  same  velocity. 
But,  supposing  the  jet  takes  place  in  the  interior  of  a 
pump -chamber  (when  the  gauge  on  the  main  indicates 
100  Ibs.  to  the  square  inch),  and  is  met  directly  or 
obliquely,  or  in  any  direction  we  like  to  imagine,  by  similar 
jets,  what  local  friction  is  set  up  ?  and  what  is  the  loss 
due  to  their  action  ?  Add  to  these  conditions  an  inter- 
mittent and  unknown  quantity  of  air,  which  is,  of  course, 
highly  compressible  together  with  solid  matter,  and  it 
will  at  once  be  realised  that  to  analyse  the  action  of  the 
elements  we  have  set  in  motion  is  a  problem  that  cut- 
and-dried  formulae  will  struggle  with  in  vain. 

Science  tells  us  that  when  a  piston  descends  into  a 
closed  chamber  containing  a  liquid,  an  equal  pressure  is 
exerted  on  each  square  inch  of  the  interior  of  that 
chamber. 

Precisely  so. 

And,  provided  there  is  a  uniform  resistance  on  each 
square  inch  of  that  interior  surface,  the  liquid  is  free 
from  frictional  resistance  of  the  water  particles.  But 
when  we  have  a  rectangular  chamber  into  which  the 
liquid  is  admitted  and  expelled  through  a  series  of  suddenly 
opened  and  closed  orifices,  it  is  clear  that  violent  streams 
and  eddies  are  produced. 

Tumultuous  conditions  exist,  which  are  without  doubt 
detrimental  to  the  efficiency  of  the  pump,  but  about 
which  little  or  nothing  is  known.  That  there  is  a  loss 
of  energy  due  to  this  cause  there  can  be  no  question, 
not  only  by  '  fluid  friction '  between  the  fluid  and  the 
walls  of  the  chamber,  but  by  the  frictional  resistance  of 
the  particles  of  the  water  or  '  loss  by  shock.'  Again, 
actual  variation  in  pressure  of  as  much  as  20  per  cent. 


6      EFFICIENCY  OF  PUMPS  AND  EJECTORS 

in  a  constant  speed  pump  clearly  demonstrates  that 
this  loss  by  shock  and  fluid  friction  is  progressive  in 
proportion  to  the  viscosity  of  the  fluid,  and  percentage 
of  solid  contained,  if  a  certain  velocity  is  exceeded. 

Opportunities  to  determine  such  problems  are  rare, 
as  the  necessary  conditions  cannot  be  reproduced  in  the 
test  house  or  laboratory ;  and  yet  until  some  advance 
in  this  science  of  friction  is  made,  one  cannot  define 
with  any  accuracy  the  cause  of  the  variations  in  pres- 
sure and  tremendous  concussions  that  occur. 

It  is  obvious,  too,  that  a  volume  of  water,  the  particles 
of  which  are  in  violent  conflict  with  each  other,  cannot 
be  impelled  under  pressure  with  the  same  power  that 
it  takes  to  impel  a  regular  stream,  as  the  kinetic  energy 
of  the  liquid  is  entirely  lost  by  the  adverse  currents  set 
up,  reacting  on  each  other,  and  creating  unknown  resist- 
ance or  negative  action.  With  moderate  pressure  and 
low  velocities,  the  negative  forces  are  of  little  import- 
ance compared  to  the  detrimental  effects  when  velocities 
are  high  and  pressure  great. 

PUMPS  :  RECIPROCATING. 

The  double-acting  plunger  pump  fitted  with  large 
rectangular  clear-way  valves  in  place  of  multiple  valves 
of  the  disc  and  grid  type  is  frequently  installed  for  raising 
sewage.  But  it  is  often  costly  in  upkeep  and  the 
chambers  do  not  readily  clear  themselves  of  solids  and 
vegetable  matter.  Neither  does  it  embody  that  essential 
feature,  extreme  simplicity,  which  gives  first  place  to 
the  single-acting  ram  pump.  The  leading  manufac- 
turers recommend  this  type,  and  there  is  little  doubt 
they  are  fully  justified  in  doing  so,  when  it  is  borne  in 
mind  that  it  is  not  the  actual  liquid  that  presents  the 
difficulties,  but  the  foreign  matter  contained  that  must 


EFFICIENCIES  AND  RECIPROCATING  PUMPS     7 

be  provided  for.  There  is  no  intention  of  dwelling  on 
the  '  power  end  '  as  that  is  a  separate  subject,  and  does 
not  affect  the  '  fluid  problem.' 

The  water  rams  may  be  operated  by  a  reciprocating 
piston  on  the  same  rod,  or  by  means  of  a  rotary  crank 
and  connecting  rod.  Hence  power  pumps  are  usually 
termed  direct  acting,  or  rotary  crank  and  flywheel 
pumps. 

The  advocates  of  the  one  type  will  vehemently  dis- 
parage the  advocates  of  the  other,  but  when  the  action 
of  the  ram  is  carefully  weighed  and  considered,  it  is 
obvious  the  rotary  motion  is  superfluous ;  and  in  the 
direct -acting  type,  whether  actuated  by  the  interposi- 
tion of  a  beam  or  not,  we  have  the  immense  advantage 
of  a  pause  at  the  end  of  each  stroke,  which  allows  the 
valves  to  close  quietly,  thus  mitigating  wear  and  tear. 
The  alleged  superiority  in  efficiency  of  the  rotary  type 
is  by  no  means  undisputed  when  it  comes  to  the  total 
expenditure  on  buildings,  plant,  and  maintenance,  especi- 
ally since  the  introduction  of  the  high  duty  compen- 
sating type.  We  have  only  to  turn  back  to  the  days  of 
the  celebrated  Cornish  pumps,  to  see  from  their  records 
that  the  duty  they  maintained  is  still  unapproachable 
by  the  vast  majority  of  the  present  day.  They  may 
indeed  be  described  as  the  parents  of  water-raising 
power  engines.  The  construction  and  action  of  the  single 
or  double-acting  reciprocating  pump  may  be  described 
as  follows. 

The  body  of  the  pump  consists  of  a  closed  chamber 
in  which  a  ram  or  plunger  reciprocates.  That  is,  it 
descends  and  rises  or  travels  backwards  and  forwards 
by  means  of  a  piston  rod,  or  the  ram  itself  passes  through 
a  water-tight  stuffing-box.  On  to  the  walls  of  this 
chamber  are  cast  or  bolted  two  hollow  covers,  one  form- 


8      EFFICIENCY  OF  PUMPS  AND  EJECTORS 

ing  the  suction  chamber  and  the  other  the  delivery 
chamber,  the  suction  pipe  and  the  delivery  pipe  terminat- 
ing therein  respectively.  In  the  divisional  walls  are  a 
number  of  orifices,  which  are  closed  by  valves  or  lids 
which  open  in  one  direction  only.  Thus  we  have  three 
chambers  distinct  from  each  other  closed  to  the  atmo- 
sphere, the  suction  chamber,  the  pump  chamber  or  body, 
and  the  delivery  chamber. 

The  action  is  as  follows.  Assuming  the  pump  to  be 
fully  charged  with  water,  the  ram  is  withdrawn,  a  vacuum 
is  formed,  and  the  water  forces  open  the  suction  valves. 
When  the  pump  chamber  is  full,  the  suction  valves 
close  and  the  ram  descends,  forcing  the  water  through 
the  delivery  valves  into  the  rising  main. 

Plate  I.  shows  the  general  arrangement  of  a  small 
(64  H.P.)  single-acting  triple  ram  pump  used  for 
discharging  crude  sewage  at  a  head  of  290  feet. 
Fig.  1  shows  a  cross  section  and  Fig.  2  a  sectional 
elevation. 

Each  barrel  is  distinct  from  the  other,  but  they  draw 
from  and  discharge  into  chambers  common  to  all  three. 

It  will  be  observed  the  position  of  the  barrels,  convex 
covers,  and  internal  surfaces  gives  us  a  compact  casting 
of  great  strength,  but  is  the  cause  of  excessive  friction 
and  must  produce  cross  currents  altogether  beyond 
defining. 

We  cannot  change  the  direction  of  a  fluid  without 
dissipating  its  energy,  i.e.  by  the  abrupt  deflection  of 
a  stream  of  water  we  lose  velocity  or  action  in  direc- 
tion of  motion. 

Now  every  action  has  an  equal  and  opposite  reaction, 
and  therefore  it  is  clear  the  less  we  change  the  direction 
of  the  fluid  stream  in  the  interior  of  the  pump  the  more 
resistance  is  reduced. 


10    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

PUMP  SUCTION. 

As  the  suction  and  all  that  appertains  to  it  is  the 
most  vital  section  of  the  whole  machine,  it  merits  first 
place  in  discussion. 

We  have,  as  it  were,  to  entice  the  liquid  into  the 
pump  chamber.  Once  there,  the  motive  power  will 
not  fail  to  send  it  forward  on  its  journey.  That  the 
pump  chamber  should  fill  with  liquid  is  of  the  utmost 
importance,  as  even  a  small  percentage  of  air  is  respon- 
sible for  violent  concussion,  the  momentum  and  inertia 
of  the  water  being  aggravated  by  the  compression  and 
expansion  of  the  air,  besides  reducing  the  discharge 
of  the  pump.  It  is  literally  impossible  to  exaggerate 
the  importance  of  the  suction  arrangements.  They 
are  the  foundation  of  the  whole  working  system. 

On  the  delivery  side  of  the  pump,  we  may  stretch  a 
point  to  suit  structural  convenience,  but  for  the  suction 
nothing  will  do  which  can  be  bettered.  We  cannot 
afford  to  disregard  a  single  item  of  knowledge  that  we 
already  possess.  The  remotest  chance  of  air  finding 
its  way  into  the  suction  must  be  rigorously  guarded 
against.  The  pipe  should  be  as  short  as  possible,  and 
well  immersed.  Every  joint  is  a  joint  too  many,  and 
every  foot  is  a  foot  too  much.  Perfection  and  absolute 
perfection  should  be  aimed  at,  even  if  it  is  not 
attained. 

SUCTION  WELLS. 

Some  engineers  attach  importance  to  the  contour  of 
the  sides  and  floor  of  the  suction  wells.  There  is  little 
doubt  this  subject  merits  attention,  especially  when 
the  sump  is  of  restricted  area  and  little  depth. 

Large  volumes  of  water  in  motion  inevitably  create 
eddies  and  disturbances  when  brought  into  contact  with 


EFFICIENCIES  AND  RECIPROCATING  PUMPS    11 

angles  and  projections  in  the  masonry.  All  these  irregu- 
larities should  be  avoided  if  a  smooth  and  even  flow  is 
desired  free  from  turbulent  and  conflicting  currents. 
Separate  wells  for  each  suction  are  a  great  convenience 
in  many  ways,  and  the  possibility  of  one  intake  inter- 
fering with  another  is  entirely  obviated. 

Am  IN  PUMPS. 

It  must  not  be  supposed  that  because  there  is  no 
actual  leak,  or  the  water  actually  below  the  rim  of  the 
intake,  that  no  air  can  enter  the  pump. 

A  drainage  effluent  in  particular  is  notoriously  highly 
aerated,  and  frequently  an  amount  of  gas  is  generated 
which  is  positively  astonishing,  especially  in  semi- 
tropical  climates.  Therefore  it  is  clear  the  liquid  is 
often  charged  with  myriads  of  minute  bubbles  or  im- 
prisoned globules  of  vapour,  These  globules  have  one 
common  ambition — that  is,  to  rise  and  free  themselves 
from  the  liquid.  The  result  is  they  unite  with  each 
other  as  they  are  drawn  into  the  pump,  and  are  caught 
or  retarded  by  any  irregularity  in  the  casting,  in  which 
they  can  lodge,  for  instance,  in  the  angles  and  beneath 
the  convex  covers. 

The  smallest  bubble  cannot  be  compressed  out  of 
existence,  and  although  in  course  of  time  they  will  '  work 
out '  unlese  there  is  an  absolute  pocket,  it  does  not 
detract  from  the  harmful  effect  they  have  already  caused. 
Hence  the  extreme  care  with  which  the  interior  lines 
of  a  pump  should  be  designed. 

There  is  little  doubt  that  air  is  the  cause  of  three- 
quarters  of  the  concussion  and  reduced  discharges, 
because  air,  being  highly  compressible  and  water  incom- 
pressible (for  practical  purposes),  the  ram  descends, 
compresses  the  air  instead  of  discharging  the  water, 


12    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

and  the  expansion  of   the  air  as  the  ram  rises  retards 
the  filling  of  the  pump  chamber. 

This  process  is  beautifully  illustrated,  if  by  accident 
or  purposely  a  hole  is  knocked  in  the  bottom  of  the  ram 
and  the  pump  drained ;  on  restarting,  it  will  then  be 
found  that  almost  the  entire  stroke  of  the  ram  is  taken 
up  in  the  compression  and  expansion  of  the  same  volume 
of  air,  without  the  admission  or  discharge  of  water 
through  the  pump  valves.  A  striking  illustration  of 
4  excessive  air '  can  also  be  observed  on  starting  a 
pump  drawing  from  a  drainage  sump  that  has  remained 
quiescent  for  some  hours  so  that  gases  are  being  freely 
liberated  on  the  surface  in  the  form  of  bubbles.  For 
the  first  half-hour  irregular  working  accompanied  by 
concussion  is  experienced  at  every  revolution  ;  but  when 
comparatively  clear  water  is  drawn,  no  matter  whether 
it  is  at  a  much  lower  level,  normal  conditions  prevail. 

MATTER  IN  PUMPS. 

Of  almost  equal  importance  to  excessive  air  is  the 
variable  percentage  of  matter  the  liquid  contains,  which, 
in  exceptional  cases,  produces  remarkable  results. 

When  a  pump,  accustomed  to  draw  and  discharge 
an  effluent  highly  charged  with  refuse  and  viscous  matter 
to  such  an  extent  that  the  interior  of  the  chambers 
and  rising  main  become  thickly  coated  with  a  glutinous 
substance,  shows  a  pressure  of  105  Ibs.  to  the  square 
inch  on  the  gauge,  and  is  called  upon  to  discharge 
clear  water  for  some  days,  the  gauge  pressure  rises 
to  125  Ibs.  to  the  square  inch,  with  corresponding 
increase  in  the  consumption  of  motive  power.  The 
interior  of  the  pump  and  suction  will  then  be  found 
perfectly  clean,  but  the  rising  main  is  still  in  a  foul 
condition.  A  circular  pipe  such  as  a  rising  main  would 


EFFICIENCIES  AND  RECIPROCATING  PUMPS    13 

naturally  be  more  difficult  to  clear  than  a  pump  chamber, 
owing  to  the  regularity  of  the  stream  and  absence  of 
turbulent  conditions,  and  the  additional  velocity,  which 
is  the  cause  of  the  extra  pressure,  is  probably  greater 
at  the  centre  of  the  stream  than  at  the  sides. 

If  the  viscosity  of  the  fluid  is  very  great,  cavitation 
and  separation  will  take  place  with  the  usual  concussion 
as  the  chambers  fail  to  fill,  and  to  remedy  this  fault 
it  would  be  necessary  to  reduce  the  speed  of  the  pump 
or  increase  the  exterior  pressure. 

STRAINER  FOR  SUCTION  PIPE. 

Suspended  matter  and  solids  are  naturally  drawn 
towards  the  intake,  and  therefore  we  must  make  pro- 
vision to  ensure  their  easy  passage  through  the  pump. 

A  rose  or  strainer  attached  to  the  pipe  rapidly  becomes 
choked,  thus  checking  the  flow  into  the  pump  chamber, 
which  is  the  worst  of  all  evils,  and  experiment  conclusively 
proves  that  a  mesh  sufficiently  fine  to  stop  canes  and 
sticks,  etc.,  is  sufficiently  fine  to  prevent  the  passage 
of  vegetable  matter.  So  the  strainer  must  be  abolished, 
and  in  its  place  a  grating  of  wide  area  should  be  pro- 
vided, and  set  up  as  far  from  the  suction  pipe  as  possible, 
the  material  and  mesh,  which  are  subjects  of  great 
importance,  being  decided  by  local  conditions. 

And  furthermore,  liberal  arrangements  must  be  made, 
either  mechanically  or  by  hand,  to  prevent  the  mesh 
or  bars  from  becoming  choked,  thus  banking  up  the 
liquid,  and  allowing  the  water  to  reach  a  dangerously 
low  level  in  the  suction  well. 

FOOT  VALVES. 

With  water  pumps  a  foot  valve  is  usually  attached 
to  the  end  of  the  suction  pipe — that  is,  immediately 


14     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

above  the  strainer.  It  consists  of  a  valve  box  contain- 
ing two  semicircular  flap  valves  with  a  common  hinge, 
and  is  for  the  purpose  of  retaining  the  water  in  the 
suction  pipe,  so  that  the  pump  can  be  easily  started. 

But  this  valve  is  an  additional  working  part,  and 
in  sewage  pumps  is  easily  made  inoperative  by  the 
finest  cane,  and  is  often  a  source  of  endless  trouble. 
Without  question  it  ought  to  be  omitted  if  circum- 
stances permit  of  fixing  a  steam  ejector  for  charging, 
otherwise  special  arrangements  must  be  made  for  rapidly 
draining  the  sump  by  independent  means,  so  that  the 
valve  can  be  cleared  by  hand. 

AIB  VESSELS. 

We  now  come  to  an  item  of  endless  controversy, 
namely,  the  air  vessel.  It  must,  however,  be  distinctly 
understood  that  these  remarks  on  this  subject  exclu- 
sively refer  to  the  type  of  pump  we  are  dealing  with 
and  the  conditions  under  which  it  works.  What  is  a 
valuable  accessory  in  one  case  is  a  superfluous  nuisance 
in  another. 

There  is  a  popular  notion,  that  an  air  vessel  absorbs 
shocks,  but  this  depends  entirely  on  the  nature  and 
origin  of  that  shock.  If  the  shock  takes  place  in  the 
body  of  the  pump  itself,  as  it  usually  does,  and  the  air 
vessel  is  placed  on  the  delivery  main,  as  it  often  is,  it 
is  incontestable,  from  the  briefest  experience,  that  what- 
ever percentage  of  the  shock  the  air  vessel  absorbs  is  a 
negligible  quantity. 

In  the  old-fashioned  slow  running  bucket  and  plunger 
pumps,  an  air  vessel  of  ample  capacity  was  a  necessity 
to  ensure  a  more  or  less  uniform  delivery.  Its  func- 
tions were,  in  fact,  to  compensate  for  the  inequality 
of  the  discharge  by  means  of  the  compression  and  expan- 


EFFICIENCIES  AND  RECIPROCATING  PUMPS    15 

sion  of  the  air  it  contained  at  each  stroke  of  the  plunger, 
but  if  the  flow  is  constant  it  is  obvious  that  its  principal 
function  ceases  to  exist. 

It  is  an  open  question  what  effect  it  has  on  a  constant 
flow,  and  the  only  use  it  can  have  is  to  rid  the  pump, 
or  rather  the  main,  of  a  certain  quantity  of  air,  that  is, 
performing  the  function  of  an  air  trap  or  pocket.  On 
the  other  hand,  with  constant  flow,  great  pressure,  and 
high  velocity,  it  often  appears  to  cause  vibration  as  the 
highly  compressed  air  simply  acts  as  a  vibrating  spring, 
magnifying  shocks  and  becoming  a  real  source  of  danger 
if  a  casting  fails,  as  the  expansion  of  the  air  causes  the 
fractured  pieces  to  fly  with  great  force. 

PUMP  VALVES. 

For  passing  crude  sewage,  the  clear-way  flap  valve 
with  leather  or  pin  hinge  or  the  multiple  clear-way 
type  are  the  only  ones  that  merit  discussion.  There 
must  be  neither  grid  nor  central  guide  to  impede  the 
passage  of  solid  matter. 

Plate  II.  shows  a  leather  -  hinged  valve.  In  large 
pumps,  five  or  six  large  rectangular  valves  of  this  type 
will  be  fixed  to  a  valve  plate,  the  valve  seats  being 
part  of  the  plate.  It  is  probable  that  the  leather- 
hinged  valve  has  been  in  use  since  the  earliest  days 
of  power  pumps,  and  it  has  indeed  a  somewhat  primi- 
tive appearance.  Nevertheless  it  may  be  regarded  as 
a  standard  design  for  sewage  at  the  present  day,  and 
at  moderate  pressure,  with  a  weak  effluent,  performs  its 
functions  in  a  more  or  less  satisfactory  manner.  But 
when  it  is  used  for  high  pressures  and  strong  sewage 
containing  quantities  of  grit  and  refuse,  its  failings 
completely  outweigh  its  advantages,  and  it  is  hard  to 
understand  how  engineers  have  rested  content  with  its 


16    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

imperfections.  At  low  pressure  it  is  true  they  are  only 
apparent  to  those  who  carefully  consider  the  action  of 
the  liquid  and  behaviour  of  the  valve  ;  but  when  the 
pressure  exceeds  a  certain  value,  the  faults  are  rapidly 
superseded  by  failures  and  its  supposed  merits  are 
converted  into  glaring  defects. 
As  this  valve  is  of  historical  interest,  let  us  analyse 

PLATE  II 


Plan 


Elevation 

LEATHER-HINGED  PUMP  VALVE 

its  construction  and  action.  Briefly,  it  consists  of  a 
wrought-iron  plate,  to  which  is  riveted  a  clack  of  leather 
by  means  of  a  wrought-iron  washer,  on  the  underside, 
sufficient  leather  being  allowed  to  project  beyond  the 
iron  plate  to  form  a  hinge.  This  tab  or  hinge  is  pierced 
by  tw^o  holes  to  correspond  to  the  studs  screwed  into 
the  lug  on  the  valve  seat.  The  foot  of  the  arm  or  stop, 


PLATE  III 


MULTIPLE  CLEAR-WAY  VALVE  PLATE  (FRONT  VIEW) 


PLATE  IV 


MULTIPLE  CLEAR-WAY  VALVE  PLATE  (BACK  VIEW) 


EFFICIENCIES  AND  RECIPROCATING  PUMPS    17 

which  controls  the  lift  of  the  valve,  forms  the  necessary 
washer,  the  whole  being  secured  in  place  by  two  nuts. 
It  will  be  observed  that  the  valve  is  without  guide,  of 
extremely  light  construction,  and  the  method  of  attach- 
ing the  leather  to  the  valve  results  in  the  forming  of 
a  cavity  on  the  underside.  Now  a  light  valve  without 
spring  is  frequently  hammered  on  to  its  seat  with  a 
crank  pump,  and  the  excessive  wear  with  irregular 
motion  leads  to  rapid  destruction  of  the  valve,  and 
the  seat  itself  will  be  battered  by  the  iron  plate. 
Saturated  leather  is  a  soft  and  pliant  material,  and,  as 
the  valve  rises  and  falls  under  pressure,  it  is  wrenched 
and  torn  by  the  fiercely  conflicting  currents  of  water. 

In  clear-water  pumps  multiple  valves  are  the  standard 
practice.  There  is  less  slip,  less  wear  and  tear,  and  a 
higher  piston  speed  is  possible,  which  all  means  in- 
creased efficiency. 

MULTIPLE  CLEAR-WAY  VALVES. 

Plate  III.  shows  the  front  view  of  a  200  horse-power 
multiple  clear-way  valve  plate.  Plate  IV.  is  the  back 
of  the  plate,  showing  its  massive  construction.  There 
are  six  of  these  to  each  pump. 

These  valves  have  a  clear  way  for  the  passage  of 
solids  and  a  leather  face,  combined  with  the  independent 
freedom  of  the  disc  valve,  but  without  the  disadvan- 
tage of  a  hinge.  They  are  so  constructed  that  they 
can  be  removed  and  replaced  on  their  seats  with  the 
hand  through  the  inspection  cover  of  the  pump,  without 
the  aid  of  spanner,  pliers,  hammer,  or  tools  of  any  descrip- 
tion. In  practice  it  has  been  found  that  these  valves 
use  six  and  a  half  times  less  leather  (owing  to  reduced 
wear)  than  the  standard  leather-hinged  type. 

They  can  be  adapted  to  almost  any  type  of  pump, 


18    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

Plate  V.  shows  a  single  valve  and  its  seat,  of  the  hori- 
zontal type.  It  will  be  observed  the  design  of  the  valve 
ensures  a  uniform  motion,  which  is  the  great  merit  of 
the  disc  type.  The  valve  consists  of  a  circular  metal 
disc  A,  on  which  is  cast  a  heavy  arm  B,  terminating 
in  two  projecting  pins  C  at  right  angles  to  the  arm  B. 
In  the  underside  of  the  arm  B  is  a  recess  D,  which  rests 

PLATE  V 


Plan  Open 


Elevation 

W*y  Pump  Valve 


Clear 

CLEAR  WAT  PUMP  VALVE 


on  a  corresponding  ridge  E  cast  on  the  back  of  the 
valve  seat  G.  On  the  upper  surface  of  the  valve  A 
are  cast  two  stops  H,  which  are  disposed  in  such  a 
manner  as  to  engage  with  the  extremities  of  the  two 
lugs  J  cast  on  the  valve  seat  G  when  the  valve  is  fully 
open. 


EFFICIENCIES  AND  RECIPROCATING  PUMPS   19 

In  this  example  a  leather  or  composition  face  K  is 
fitted  to  the  underside  of  the  valve,  by  means  of  the 
combined  stud  and  washer  L.  By  this  means  it  is  clear 
the  face  K  can  be  easily  replaced. 

It  is  obvious  that  as  the  valve  is  lifted  by  the  fluid 
the  space  between  the  lugs  /  forms  the  guide  in  which 
the  arm  B  works,  thus  obviating  all  chance  of  side  motion. 
The  recess  D  resting  on  the  ridge  E  prevents  the  valve 
from  having  any  tendency  to  slip  either  forward  or 
backward  when  closed.  Furthermore,  by  this  means 
we  obtain  a  maximum  aperture  at  one  extremity  of  the 
valve  with  a  minimum  turning  motion  at  the  other. 
Also,  it  must  be  noted,  any  wear  taking  place  at  the 
point  of  contact  D  does  not  affect  the  water -tightness 
of  the  valve  face  upon  the  seat  as  the  valve  is  entirely 
free  to  the  pressure  exerted  by  the  fluid.  When  the 
valve  is  in  operation,  arm  B  slides  backward  as  it  rises 
and  the  pins  C  are  of  a  necessity  depressed. 

At  its  maximum  opening  the  valve  is  absolutely 
rigid  with  the  seat  by  reason  of  the  stops  H  engaging 
with  the  lugs  J  at  the  points  1  and  2  and  the  pins  C  at 
3  and  4 — that  is,  six  points  in  all. 

To  remove  the  valve  from  its  seat  the  front  must  be 
kept  depressed  while  the  pins  C  are  raised ;  at  the  same 
time  the  whole  disc  is  pushed  backward  till  the  point 
M  comes  in  contact  with  the  underside  of  the  lug  J, 
when  it  will  be  found  that  the  pins  C  are  clear  of  the 
projection  N. 

By  continuing  to  raise  the  pins  C  and  keeping  the 
front  of  the  valve  depressed,  the  whole  disc  can  now 
be  drawn  forward,  the  pins  C  sliding  over  the  back  of 
the  lugs  J  by  reason  of  the  curve  0,  and  thus  the  arm 
B  is  easily  withdrawn  from  the  guide. 

To  replace  the  valve  the  reverse  process  is  required, 


20    EFFICIENCY  OP  PUMPS  AND  EJECTORS 

and  the  projection  P  prevents  the  valve  from  coming 
to  rest  in  a  faulty  position. 

Although  this  description  may  appear  complex,  it 
is  not  difficult  to  see  that  in  practice  the  operation  of 
removing  the  valve  cannot  exceed  a  few  seconds,  even 
when  situated  in  a  totally  inaccessible  place,  to  the 
ordinary  type. 

Plate  VI.  shows  the  front  and  side  view  of  a  rect- 
angular form  of  multiple  clear-way  valve  for  a  large 
sewage-pump  valve  plate. 

The  plate  is  a  large  one  and  originally  contained  33 
valves  in  11  rows,  with  three  valves  to  each  row. 

It  will  be  observed  the  plate  now  contains  70  valves 
in  10  rows,  with  seven  valves  to  each  row,  with  a  guide  to 
each  valve  and  no  hinge  pin  to  wear. 

Plate  VII.  shows  another  design,  consisting  of  a  nest 
of  four  valves,  which  have  been  substituted  for  a  single 
9-in.  double-flap  valve,  set  horizontally  in  the  pump 
chamber  of  a  direct-acting  plunger  pump. 

In  pumps  of  the  largest  dimensions,  which  contain 
many  scores  of  valves,  the  enormous  saving  in  time  and 
labour  alone  resulting  from  the  adoption  of  a  design 
which  can  be  removed  and  replaced  with  such  ridicu- 
lous ease,  instead  of  by  the  old  method  of  extracting 
pins  and  manipulating  obstinate  nuts  eroded  by  the 
action  of  the  effluent,  is  too  obvious  to  need  dilation. 

From  a  superficial  inspection  of  the  drawing  it  would 
appear,  at  first  sight,  that  the  valve  would  not  retain 
its  position,  but  the  pressure  of  the  water  on  the  under- 
side is  so  exerted  that  the  front  of  the  valve  cannot 
avoid  being  lifted,  in  which  case  the  opposite  extremity 
is  bound  to  be  depressed,  neither  can  the  liquid  impart 
the  necessary  consecutive  movements  to  free  the  valve 
from  its  true  working  position.  Hence  it  may  be  described 


PLATE  VI 


MULTIPLE  CLEAR-WAT  VALVE  PLATE 


EFFICIENCIES  AND  RECIPROCATING  PUMPS    23 

as  an  independent  clear-way  multiple  valve,  as  there  is 
neither  nut,  screw,  nor  pin  that  attaches  the  disc  to  the 
seat.  The  necessity  for  large  inspecting  covers  for  the 
purpose  of  inserting  and  manipulating  tools  may  be 
abolished,  as  the  valve  can  be  placed  in  position  and 
extracted,  even  when  covered  with  liquid  in  a  confined 
position.  This  valve,  it  will  be  noted,  is  of  heavy 
construction,  and  the  leather  face  is  kept  in  position 
by  a  single  mushroom-headed  stud,  which  not  only 
deflects  the  liquid  with  a  minimum  of  friction  but  allows 
the  leather  to  be  replaced  in  a  few  minutes. 

If  we  bear  in  mind  that  there  is  100  Ibs.  to  the  square 
inch  above  the  valve  as  well  as  below  it,  and  if  the  area 
is  sufficient  to  easily  pass  the  required  volume,  there  is 
no  reason  to  assume  that  excessive  leverage  exists. 
After  two  years'  work  at  290  ft.  head  these  valves 
showed  no  scoring  or  defects. 

This  valve  under  heavy  pressure  with  '  a  gritty ' 
liquid  is  undoubtedly  superior  in  water-tightness  and 
length  of  life  to  the  leather-hinge  type,  and  the  merits 
of  the  multiple  valve  over  the  old-fashioned  rectangular 
sewage  valve  in  durability  and  efficiency  are  too  well 
known  to  be  repeated. 


CHAPTER  II 
CENTRIFUGAL  PUMPS  AND  EJECTORS 

CENTRIFUGAL  PUMPS. 

THE  centrifugal  pump  finds  much  favour  in  certain 
localities  where  the  liquid  is  in  great  volume  with  a 
low  head,  short  delivery,  and  uniform  working  conditions. 

It  has  the  immense  advantage  of  being  without  valves  ; 
but  the  drawbacks  are  of  such  a  description  that  it  is 
not  expedient  to  install  them  unless  the  precise  nature 
of  the  work  it  will  have  to  do  can  be  stated. 

It  is  a  fixed  mathematical  calculation  which  neither 
permits  of  modification  in  speed,  additional  head,  or 
mechanical  wear  without  impaired  efficiency.  When 
very  large  volumes  have  to  be  dealt  with  at  low  heads, 
the  mechanical  wear  is  insignificant ;  but  in  small  pumps 
of  this  class  a  high  efficiency  rapidly  disappears.  Again, 
if  it  is  called  upon  to  deal  with  a  viscous  fluid  and  the 
friction  is  increased,  it  will  practically  cease  to  discharge. 
The  centrifugal  pump  is,  however,  without  doubt  the 
most  popular  method  of  raising  sewage,  and  is  particu- 
larly well  adapted  to  a  motor  drive,  or  a  belt  drive  from 
small  internal-combustion  engines. 

It  is  cheap  to  install  and  gives  a  good  mechanical 
efficiency  on  trial. 

In  these  pumps  a  constant  velocity  is  imparted  to  the 
liquid  in  a  suitably  designed  casing,  by  means  of  an 
impeller,  consisting  of  a  hollow  disc  which  is  divided 
into  passages  or  ducts  by  means  of  radial  vanes  or  blades 
disposed  in  such  a  manner  that  the  water  enters  the 


CENTRIFUGAL  PUMPS  AND  EJECTORS      25 

centre  of  the  disc,  and  is  expelled  from  the  perimeter 
when  the  disc  or  impeller  is  revolved  at  a  high  speed. 
This  disc  must  rotate  truly  in  its  casing,  and  a  machined 
surface  is  provided  on  the  exterior  of  the  impeller  to 
coincide  with  a  similar  machined  surface  on  the  inside 
of  the  casing  to  prevent  the  expelled  liquid  returning 
to  the  suction  pipe.  That  is  to  prevent  '  slip.'  It 
will  readily  be  seen  that  if  these  points  of  contact  or 
fine  clearance  become  worn  by  sand  and  grit,  excessive 
'  slip  '  will  take  place.  / 

The  action  set  up  is  uniform,  the  flow  constant,  but 
unless  a  fine  screen  is  provided,  small  or  high  lift  pumps 
of  this  description  are  liable  to  frequent  stoppage  from 
rubbish  and  solid  substances  becoming  firmly  wedged 
in  the  impeller  ducts  and  fibrous  matter  fouling  the 
internal  clearances. 

When  such  pumps  are  coupled  direct  to  the  power 
engine  they  form  compact  units,  require  light  founda- 
tions, and  are  economical  in  engine-room  space.  On 
the  other  hand,  many  engineers  prefer  to  erect  them 
below  the  level  of  the  water  in  the  suction  well,  in  which 
case  deep  excavations  and  heavy  masonry  chambers  are 
required. 

CENTRIFUGAL  PUMPS'  VERTICAL  SHAFT. 

In  such  cases  the  motors  are  arranged  on  the  engine- 
house  floor  and  connected  to  the  pumps  by  vertical 
shafts. 

The  pumps,  of  course,  are  turned  over  and  the  im- 
pellers revolve  in  a  horizontal  plane.  To  take  the  weight 
of  the  shaft  a  thrust  block  is  provided  above  the  pump, 
and  forced-water  lubrication  is  required.  Such  installa- 
tions are  extremely  neat  in  appearance,  and  for  clear 
water  are  to  be  preferred  in  many  ways. 


26    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

For  sewage  it  is  doubtful  if  they  are  more  satisfactory 
than  the  usual  type,  as  it  is  necessary  to  have  a  pump 
that  can  be  easily  opened,  and  the  vertical  shaft  has  to 
be  completely  dismantled  before  this  can  be  done.  In- 
spection covers  are  provided  in  the  pump  casing  ;  but 
it  will  be  found  impossible  to  clear  the  impeller  ducts  of 
pieces  of  wood  and  like  articles  through  such  small  hand 
openings.  For  some  reason  fibrous  matter  collects  in 
large  balls  round  the  nut  which  holds  the  impeller  in 
position,  and  the  grit  in  the  effluent  cuts  deeply  into 
the  shaft  under  the  rotating  action.  It  must  also  be 
remembered  they  require  sumps  to  draw  from,  and 
screening  chambers  and  the  necessary  mechanical  appli- 
ances connected  therewith. 


PNEUMATIC  EJECTORS  IN  TUBBINGS. 

Comparatively  speaking,  the  pneumatic  ejector  is  an 
obscure  apparatus  compared  to  a  pump. 

Plate  VIII.  shows  a  typical  example  of  a  pair  of 
ejectors  in  a  cast-iron  tubbing  sunk  in  water-logged  soil 
consisting  of  rubbish,  clay,  and  sand. 

These  tubbings  are  sunk  with  compressed  air  to  a 
predetermined  depth  below  the  proposed  invert  level  of 
the  sewer  manhole.  In  this  example  the  depth  sunk 
from  the  surface  to  the  cutting  edge  is  about  25  feet.  In 
some  cases  the  floor  of  the  tubbing,  which  is  composed 
of  box-section,  cast-iron  plates,  filled  with  concrete,  is 
subjected  to  an  external  pressure  of  100  tons.  The  inlet 
manhole  seen  to  the  left  of  the  tubbing  is  17  feet  deep, 
from  the  invert  of  which  the  horizontal  cast-iron  inlet 
pipe  passes  through  the  tubbing  wall  to  the  ejectors. 
The  delivery  pipe  passes  out  through  the  cone  to  the 
sealed  sewage  main,  which  discharges  into  the  main 


PLATE  VIII 


EJECTORS  IN  CAST-IRON  TUBBING 
(Sharia,  Clot  Bey,  Cairo) 


CENTRIFUGAL  PUMPS  AND  EJECTORS      27 

collecting  sewer,  possibly  two  miles  distant,  or  direct 
to  the  disposal  works  by  a  main  sealed  sewer. 

The  air  main  enters  the  chamber  through  the  upper- 
most ring  shown  to  the  left,  and  the  exhaust  passes  out 
at  the  same  level  to  the  silencing  chamber,  consisting  of 
a  length  of  24-inch  cast-iron  pipe  (not  shown),  and  thence 
to  the  atmosphere  by  means  of  the  vertical  steel  column 
standing  on  the  foot  walk.  The  entrance  to  the  tubbing 
is  effected  by  a  hinged  cover  at  street  level. 

SUBSIDIARY  EJECTORS. 

Where  ejector  stations  are  situated  in  such  localities 
that  they  would  require  a  greater  pressure  to  discharge 
the  sewage  than  the  maximum  maintained  at  the  power 
house,  the  sealed  sewage  rising  mains  empty  into  gravi- 
tation sewers,  and  the  sewage  is  re-ejected  a  second  time. 

Such  ejectors  are  subsidiary  ejectors,  of  which  there 
may  be  any  number  of  stations. 

DESCRIPTION  OF  EJECTORS. 

Briefly,  the  ejectors  consist  of  spherical  vessels  of 
cast  iron  or  steel  from  50  to  500  gallons  (or  larger)  in 
capacity  (Plate  IX.),  into  which  the  sewage  flows  by 
gravitation. 

When  full,  the  compressed  air  is  automatically  admitted 
and  shut  off  as  the  contents  are  discharged. 

They  are  arranged  in  pairs,  as  shown  on  Plate  X.,  and 
work  alternately  or  differentially,  according  to  the 
volume  of  the  sewage  to  be  dealt  with  ;  but  either  of 
the  two  can  be  entirely  shut  off  without  interference  to 
the  other's  working. 

In  this  diagram  (Plate  X.)  the  ejector  marked  NS  is 
full,  the  alternating  valve  A  and  the  automatic  valve  B 
are  open,  and  the  air  about  to  discharge  the  contents, 


X 


CENTRIFUGAL  PUMPS  AND  EJECTORS      29 

while  ejector  OS  is  filling.  The  automatic  valve  C  shows 
the  air  port  closed  and  the  exhaust  open.  These  three 
valves,  A,  B,  C,  are  controlled  by  the  slide  valves  in  the 
air  chests  marked  Z>,  E,  under  full  pressure  from  the  main. 
These  slide  valves  are,  in  turn,  actuated  by  the  weighted 
lever  attached  to  the  rod  passing  through  the  crown  of 
the  ejector,  to  which  a  '  bell '  or  float  F  is  attached  and 
a  weight  O  is  suspended. 

It  is  clear,  as  the  liquid  rises  and  falls,  the  slide  valve 
must  take  up  one  of  two  positions,  thus  alternately 
releasing  the  air  from  either  end  of  the  piston  valve 
cylinders.  It  will  be  observed  the  rise  of  the  float  F 
does  not  check  the  flow  of  the  liquid  into  the  ejector, 
but  the  admission  of  the  air  through  the  valves  A,  B  or 
A,  C  pressing  on  the  sewage. 

The  valve  A,  being  able  to  take  up  one  of  two  posi- 
tions only,  the  ejectors  cannot  discharge  together, 
but  they  can  fill  together,  and  the  one  or  the  other  of 
the  two  ejectors  must  wait  upon  its  fellow  to  empty 
before  the  valve  A  is  thrown  over,  though  the  valves 
B  and  C  may  have  both  air  ports  open  together.  Thus 
the  ejectors  may  discharge,  alternately  or  differentially, 
according  to  the  volume  of  sewage  to  be  dealt  with . 

ACTION  OF  EJECTORS  ON  SEWAGE. 

As  a  rule  ejectors  are  designed  to  fill  and  discharge 
in  one  minute  ;  but  in  many  cases  this  rate  can  be  greatly 
exceeded,  according  to  the  head  of  water  in  the  rising 
main  and  the  air  pressure  available. 

It  will  be  observed,  from  the  design  of  this  apparatus, 
the  compressed  air  exerts  the  necessary  pressure  directly 
on  the  surface  of  the  liquid,  till  it  has  been  discharged 
through  an  outlet  in  the  base  of  the  ejector.  By  this 
means  all  heavy  matter  is  first  expelled,  having  the 


CENTRIFUGAL  PUMPS  AND  EJECTORS      31 

full  volume  of  water  behind  it  to  carry  it  through  the 
valves  and  rising  main.  This  is  precisely  what  a  pump 
is  unable  to  effect.  Again,  the  ejector  is  ready  to  take 
the  merest  dribble  or  the  maximum  flow  at  a  moment's 
notice. 

The  arrangement  of  the  inlet  and  discharge  pipes  and 
valves  can  be  clearly  seen  in  Plate  X.  The  action  of  the 
inlet  or  '  suction  '  and  delivery  valves  is  steady.  There 
are  no  machined  parts  or  internal  bearings  in  contact 
with  the  liquid.  There  is  no  concussion  or  loss  by  shock 
from  air  or  gas,  as  the  ejector  fills  by  gravitation  against 
the  atmosphere  and  discharges  with  a  steady  pressure. 
The  direction  of  motion  is  constant :  no  cavitation  or 
separation  can  take  place. 

There  is  neither  centrifugal  nor  reciprocating  action 
to  cause  loss  of  velocity  by  deflection.  The  compressed 
air  is  the  impeller  or  piston.  Comparatively  speaking, 
there  is  nothing  to  repair,  and  there  is  nothing  to  wear 
out.  It  appears  to  be  the  most  suitable  mechanical 
apparatus  devised  for  raising  crude  sewage,  viz.  a  '  liquid 
or  viscous  fluid,  containing  every  conceivable  substance 
and  variety  of  refuse,  which  may  cause  obstruction  or 
destruction  to  mechanical  parts.' 

The  limitations  of  the  ejector  are  entirely  due  to  the 
difficulty  of  obtaining  a  good  mechanical  efficiency  when 
using  compressed  air  as  a  motive  fluid  at  high  pressure 
without  expansive  working.  The  greater  the  pressure 
the  greater  the  volume  of  air  required  to  raise  a  given 
quantity  of  water,  and  the  lower  the  mechanical  effici- 
ency ;  therefore,  the  higher  the  fuel  cost. 

LOCALITIES  CLASSIFIED. 

Before  proceeding  to  describe  further  details  of  the 
various  systems  employed  for  raising  sewage  and  the 


32    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

efficiencies  they  give,  it  is  well  to  roughly  classify  the 
localities  for  which  they  are  suitable,  as  it  is  obviously 
unjust  to  compare  one  method  or  machine  with  another 
if  it  is  selected  to  perform  certain  work  it  was  never 
intended  to  do. 

On  the  other  hand,  whether  a  pump  or  ejector  is  in- 
stalled they  are  both  constructed  of  the  same  materials 
and  subject  to  the  same  chemical  action ;  therefore  the 
installations  selected  for  comparison  should  be  discharg- 
ing the  same  effluent,  assuming,  of  course,  the  apparatus 
has  been  made  and  supplied  for  the  work  it  is  set  to  do. 

It  is  exceptional  to  find  representative  types  of  all 
three  of  the  methods  enumerated  above  in  a  single 
sewage  scheme,  and  herein  lies  much  of  the  value  of 
the  observations  and  diagrams  hereafter  recorded  and 
classified. 

The  conditions  of  locality  may  be  roughly  divided  as 
follows  : 

No.  I.  Situation  where  the  natural  fall  of  the  ground 
enables  the  whole  volume  of  sewage  to  flow  by  gravi- 
tation to  a  selected  site  near  the  city,  from  which  site 
it  is  pumped  with  a  maximum  '  head  '  of  40  feet  to  the 
disposal  works. 

No.  2.  Situation  as  above  where  the  *  head '  does 
not  exceed  90  feet. 

No.  3.  Situation  as  above  where  the  head  exceeds  90  feet. 

No.  4.  Situation  where  there  is  no  natural  fall,  possibly 
a  water -logged  soil  and  prohibitive  reasons  for  laying 
deep  sewers. 

MACHINERY  :  SUITABLE  CONDITIONS. 

Situation  No.  I.  If  large  volumes  of  diluted  sewage 
have  to  be  raised  with  a  short  length  of  delivery  main, 
the  centrifugal  pump  may  prove  to  be  the  most 


CENTRIFUGAL  PUMPS  AND  EJECTORS      33 

economical,  from  the  commercial  point  of  view.  But 
the  depreciation  in  small  units  dealing  with  a  gritty 
effluent,  such  as  road  washings,  etc.,  besides  domestic 
sewage,  is  so  rapid  that  the  pneumatic  ejector,  though 
more  costly  in  the  first  place,  will  be  found  more  econo- 
mical over  a  number  of  years.  The  absence  of  sump 
and  screening  chamber  also  enables  the  ejector  station 
to  be  situated  in  the  centre  of  the  town  if  necessary, 
without  offence  or  inconvenience.  In  many  cases  the 
effluent  does  not  have  to  be  lifted  more  than  20  feet,  or 
when  discharging  into  the  sea  5  feet  or  6  feet.  In  such 
cases  the  difference  in  first  cost  may  amount  to  a  large 
figure. 

Situation  No.  2.  Under  such  conditions  there  is  almost 
certain  to  be  a  considerable  length  of  rising  main.  With 
short  mains  centrifugal  pumps  might  be  installed,  each 
pump  having  its  own  main ;  but  the  double-acting 
plunger  pump  would  probably  be  the  most  efficient  in 
such  a  situation. 

Several  units  can  pump  into  the  same  main,  and  such 
an  installation  can  deal  with  a  great  variation  in  flow 
under  exacting  conditions.  Within  recent  years,  how- 
ever, makers  have  placed  ejector  installations  on  the 
market  for  which  they  claim  a  high  efficiency  at  92  feet 
head,  and  when  the  effluent  to  be  dealt  with  is  strong  this 
should  be  taken  into  consideration  in  competition  with 
the  plunger  pump,  as  it  will  be  shown  in  a  later  chapter, 
that  the  commercial  efficiency  of  the  pump  is  not  so 
much  greater  than  that  of  the  ejector. 

Situation  No.  3.  For  a  head  of  water  above  90  feet  the 
single-acting  ram  pump  is  usually  selected  without 
hesitation.  The  outside  packed  rams  enable  any  wear 
to  be  taken  up  and  a  water-tight  joint  maintained.  In 
mechanical  efficiency  it  is  unsurpassed,  and  its  com- 

C 


34     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

mercial  efficiency  is  largely  a  matter  of  care  and  atten- 
tion. Like  all  other  pumps,  though,  it  requires  a  sump 
and  screening  chamber,  and  must  be  situated  well  out- 
side the  precincts  of  the  city. 

Situation  No.  4.  As  a  rule  such  conditions  entail  a 
somewhat  higher  capital  cost  for  machinery,  but  a  reduced 
cost  in  laying  sewers.  It  is  in  such  situations  that  the 
pneumatic  ejector  is  invaluable.  The  area  to  be  drained 
is  divided  up  into  sections  according  to  local  require- 
ments, and  at  the  lowest  point  of  each  area  a  masonry 
chamber  is  built,  or  a  cast-iron  tubbing  is  sunk  in  which 
to  place  the  ejectors. 

These  chambers  are  connected  by  compressed-air 
mains  to  the  air-compressing  power  house,  which  may 
be  situated  on  any  convenient  site,  as  it  is  no  more 
offensive  than  a  tramway  power  house  or  an  electric 
generating  station.  The  ejector  stations  may  be  situated 
directly  beneath  the  streets,  as  shown  in  Plate  VIII., 
as  there  is  no  offensive  sump  or  screening  chamber. 

When  a  large  number  of  ejector  stations  are  required 
there  is  usually  a  main  artery  into  which  the  sealed 
sewage  pressure  mains  from  the  ejectors  discharge. 

In  cities  that  cover  extensive  areas,  it  is  usually  found 
advisable  to  provide  subsidiary  ejector  stations,  that  is, 
one  station  discharging  into  another,  in  order  to  equalise 
the  working  pressure  that  must  be  maintained  at  the 
power  house.  In  practice,  55  feet  to  65  feet  head  is  the 
maximum  for  economical  working,  but  45  feet  is  to  be 
preferred,  the  frictional  head  of  the  cast-iron  main 
accounting  for  a  large  percentage  of  the  pressure.  But 
the  outstanding  merit  of  this  system  is  the  absence  of 
sumps  or  any  accumulation  of  sewage.  The  effluent 
is  discharged  as  soon  as  it  arrives  from  the  sewers,  and 
no  decomposition  can  take  place. 


CENTRIFUGAL  PUMPS  AND  EJECTORS      35 

SECTIONAL  SYSTEMS  :  ALTERNATIVES. 

From  time  to  time  various  methods  have  been  sug- 
gested and  demonstrated,  with  a  view  to  retaining  the 
advantage  of  the  ejector,  but  eliminating  one  of  the 
principal  drawbacks,  which  is  leakage  from  the  air 
mains.  That  is  to  say,  it  is  not  the  ejector  with  which 
fault  is  found,  but  the  difficulty  of  efficiently  transmit- 
ting the  secondary  power  to  operate  the  machine.  It 
must  not  be  overlooked,  though,  that  the  secondary 
power  is  directly  applied  to  the  work  and  is  not 
converted  into  mechanical  motion :  thus  the  mechanical 
friction  is  eliminated. 

HYDRAULIC  SYSTEM. 

In  order  to  avoid  air-main  losses  some  engineers 
favour  the  hydraulic  system.  Apparatus  to  raise  the 
sewage  is  operated  by  water  at  high  pressure,  supplied 
from  a  central  station,  and  distributed  by  means  of 
cast-iron  mains  to  the  sewage  pumping  stations. 
It  has  been  in  use  many  years  but  has  not  been 
widely  adopted,  though  exceptional  local  conditions  may 
demonstrate  it  as  more  economical  than  the  pneumatic 
system. 

To  substitute  a  high -pressure  water  main  for  a  low- 
pressure  air  main  may  result  in  economy  in  the  trans- 
mission of  power  ;  but  it  is  a  question  whether  it  is 
economically  sound  to  install  high-pressure  machinery 
and  its  accessories  greatly  in  excess  of  what  is  required 
in  the  class  of  work  we  are  dealing  with.  Again,  unless 
a  water  supply  of  remarkable  purity  is  available,  there 
will  nearly  always  be  some  fouling  of  working  parts, 
or  deposit,  which  with  compressed  air  is  entirely 
absent. 


36     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

CENTRIFUGAL  PUMPS  :  MULTIPLE  SYSTEM. 

Within  recent  years  many  attempts  have  been  made 
to  employ  small  centrifugal  pumps  in  place  of  ejectors, 
but  they  require  considerable  attention  and  are  un- 
certain to  depend  on  for  automatic  action.  A  central 
power  station  is  required  for  generating  the  necessary 
current  to  drive  the  motors  which  actuate  the  pumps, 
and  a  system  of  distributing  cables,  in  place  of  air  or 
water  mains,  for  transmitting  the  power. 

The  pumps  are  placed  below  the  level  of  the  collecting 
manhole,  or  enclosed  container,  and  automatic  arrange- 
ments for  starting  and  stopping  are  employed.  It  is 
claimed  for  such  pumps  that  no  screening  of  the  sewage 
is  required,  but  no  pump  can  retain  its  efficiency  for 
any  length  of  time  when  called  upon  to  deal  with  road 
metal,  bricks,  tins,  broken  metal,  etc. ;  on  the  other 
hand,  the  ejector  suffers  no  loss  of  efficiency  from  passing 
such  articles. 

The  principal  merit  of  the  electric  transmission  is 
that  there  is  no  loss  of  efficiency  by  leakage,  as  there 
is  in  the  air  mains.  On  the  other  hand,  there  is  the 
friction  of  the  motor  and  pump  to  be  taken  into  con- 
sideration. In  first  cost  little  economy,  if  any,  would 
be  realised,  as  cables,  switches,  and  their  accessories 
are  constructed  of  expensive  materials. 

Again,  there  are  some  advocates  of  a  sectional  multiple 
centrifugal  pump  system,  operated  from  a  central 
generating  station,  as  just  described,  in  which  the  object 
is  to  dispense  with  long  lengths  of  rising  main.  By 
such  means,  it  is  claimed,  frictional  head  is  practically 
eliminated,  and  the  whole  power  employed  is  utilised 
to  raise  the  sewage  to  the  required  level. 

To  effect  this,  three  or  four  collecting  stations  are 


CENTRIFUGAL  PUMPS  AND  EJECTORS      37 

provided  in  place  of  one,  each  station  being  provided 
with  motor  pumps  in  duplicate,  placed  in  a  chamber 
alongside  the  sump  from  which  they  draw. 

The  pumps  raise  the  effluent  to  a  high-level  gravita- 
tion sewer  in  close  proximity  to  the  station,  from  which 
it  flows  to  the  next  station  to  be  repumped,  till  it  is 
discharged  at  the  outfall.  Screens  are  dispensed  with 
in  the  sumps,  but  provision  has  to  be  made  for  removing 
heavy  articles. 

The  pumps  themselves  are  of  special  construction 
and  cut  up  or  disintegrate  fibrous  vegetable  matter, 
cotton  waste,  discarded  cloths,  and  materials  of  a  similar 
nature,  therefore  there  must  be  a  margin  of  power  over 
that  reqiiired  to  actually  lift  the  effluent  to  the  required 
level.  In  the  case  of  the  pneumatic  ejector  such  material 
is  simply  carried  forward  by  the  velocity  of  the  water, 
without  being  subjected  to  violent  action.  In  order  to 
enable  the  suction  pipe  of  such  pumps  to  draw  from  the 
sump  without  becoming  choked  or  obstructed  with 
sticks,  etc.,  the  suction  orifice  consists  of  a  slit,  by  which 
means  it  is  claimed  vegetable  matter  easily  passes  but 
excludes  large  objects  that  might  choke  the  pump.  It 
is  an  open  question  whether  there  is  any  appreciable 
loss  from  friction  due  to  this  form  of  suction  orifice  ; 
but  the  difference  between  a  plain  termination  of  a 
circular  pipe  for  suction  purposes  and  the  recognised 
standard  bell  mouth  is  well  known.  However,  in  raising 
crude  sewage,  hard  and  fast  rules  may  often  be  aban- 
doned without  detrimental  results,  though  it  is  as  well 
not  to  travel  too  far  from  traditional  practice,  and  all 
modifications  should  be  as  much  as  possible  in  accord 
with  science. 

Arrangements  are  made  to  automatically  start  and 
stop  the  motors  by  means  of  floats,  actuated  by  the  rise 


38     EFFICIENCY  OF  PUMPS  AND  EJECTOKS 

and  fall  of  the  sewage.  Thus,  when  the  sump  contains 
a  certain  depth  of  water  the  pump  starts  ;  when  the 
water  has  fallen  to  a  certain  predetermined  level  the 
pump  stops.  The  advantages  of  eliminating  the  friction 
in  the  rising  main  are  very  great ;  but  we  have  to  remember 
there  is  a  certain  amount  of  increased  mechanical 
friction  from  running  three  or  four  sets  of  motors  and 
pumps  in  place  of  one  or  two  units.  There  is  also  the 
additional  capital  cost,  increased  maintenance  and 
stores,  and  repairs  in  proportion. 

The  gravitation  pumping  mains  also  serve  as  sewers, 
and  are,  of  course,  kept  constantly  flushed.  On  the 
other  hand,  in  countries  where  decomposition  of  the 
effluent  sets  in  very  rapidly,  a  number  of  sumps  dotted 
about  a  city  are  open  to  objection  from  the  sanitary 
point  of  view,  and  even  some  danger  to  employees. 

SUMPS  :  DANGERS  FROM  GAS. 

No  matter  what  automatic  devices  may  be  employed 
for  removing  heavy  objects,  or  type  of  catch -pit  that 
can  be  raised  to  the  surface,  it  becomes  necessary  at 
times  for  men  to  descend  them  and  run  the  risk  of 
losing  their  lives  from  foul  gases.  In  semi-tropical 
climates  these  gases  generate  with  great  rapidity,  and 
every  hand  employed,  either  cannot,  or  will  not  take 
those  precautions  of  which  he  does  not  see  the  use. 

Most  engineers  can  give  instances  of  loss  of  life  from 
men  descending  sumps  and  manholes,  even  in  cases 
where  gas  has  never  been  suspected  till  the  man  has 
failed  to  reappear. 

As  an  example,  a  new  manhole  had  recently  been 
completed  which  was  connected  to  an  ejector  station. 
Neither  the  ejector  nor  the  sewer  was  in  use,  but  the 
manhole  contained  3  feet  or  4  feet  of  infiltration  water. 


CENTRIFUGAL  PUMPS  AND  EJECTORS      39 

The  ejector  was  started,  the  water  drained  off,  with 
a  few  discharges,  and  it  was  observed  that  the  mason 
had  left  a  brick  on  the  benching  some  days  previously. 
One  of  the  men  present  descended  to  remove  it,  and  his 
mate  guarding  the  entrance  happened  to  engage  a  friend 
in  conversation.  Wondering  at  the  delay  in  the  man's 
reappearance  he  looked  down  the  manhole,  and  observed 
his  comrade  was  prostrate  at  the  bottom,  and,  though 
brought  to  the  surface  immediately,  could  not  be  revived. 

SUMPS  :  DANGERS  FROM  EXPLOSION. 

At  times  it  is  also  exceedingly  dangerous  to  lower 
naked  lights  into  manholes  and  sumps,  and  examples 
could  be  given  of  several  men  being  killed  and  injured 
by  a  single  explosion.  Numerous  sewage  sumps  should 
be  avoided,  especially  in  cities  where  they  have  to  be 
covered  in  and  do  not  have  free  ventilation.  No  drainage 
scheme  which  embodies  dangerous  features  should  be 
recommended  if  an  alternative  exists  of  equal  merits, 
even  at  some  saving  in  first  costs. 

ELECTRIC  MOTORS. 

The  average  type  of  electric  motor  placed  in  an 
underground  chamber  is  often  far  from  reliable.  The 
damp  atmosphere  tends  to  corrode  all  bright  surfaces, 
and  if  shocks  occur,  or  there  is  a  heavy  overload,  the 
motor  may  be  seriously  injured. 

If  large  powers  are  required,  a  high  voltage  must  be 
employed  or  the  motor  will  be  heavy  and  costly,  and 
with  high  voltage  there  is  always  the  danger  of  a  fatal 
accident  unless  highly  paid  men  are  employed. 

The  very  ease  and  simplicity  with  which  a  motor  can 
be  started  and  stopped  breeds  contempt  for  caution, 
and  sooner  or  later  a  cleaner  will  accidentally  touch  a 


40     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

live  wire,  neglect  a  safety  switch,  or  make  some  other 
omission  which  will  cost  him  his  life.  There  is  no 
warning — he  is  killed  instantaneously. 

A  motor  is  a  difficult  and  costly  thing  to  repair,  and 
as  a  rule  it  does  not  pay  to  keep  a  highly  skilled  man 
who  is  competent  to  rewind  an  armature  that  has  been 
burnt  out  or  turn  up  a  commutator. 

MOTORS'  RELIABILITY. 

In  well-built  engine  houses,  motors  will,  of  course,  run 
for  years,  with  practically  no  repairs  and  a  minimum 
of  attention  ;  but  for  all  that,  when  the  critical  time 
arrives,  and  the  installation  has  to  perform  its  work 
under  unforeseen  conditions  (it  may  be  once  in  a  number 
of  years),  they  are  more  liable  to  be  put  completely  out 
of  action  by  some  trifling  mishap.  Unless  an  engineer 
has  had  various  types  of  machinery  under  his  personal 
supervision  for  long  periods,  it  is  not  easy  to  appreciate 
this  fact. 

Let  us  take  an  actual  example  to  demonstrate  this 
contention.  In  the  Cairo  system  of  drainage,  steam- 
driven  compressors  supply  the  ejector  stations  with 
compressed  air.  A  separate  plant,  consisting  of  direct- 
coupled  compound  steam-engines  and  dynamos,  supply 
current  to  electric  motors  for  driving  the  main  con- 
densing-plant  air  and  circulating  pumps,  besides  supply- 
ing current  to  a  motor  pump  situated  in  the  grounds 
for  renewing  the  water  in  the  cooling  pond. 

In  addition  to  the  ejectors,  a  special  storm-water 
pumping  station  is  provided,  containing  motor  centri- 
fugal pumps,  supplied  with  current  from  the  Electric 
Light  Company's  mains. 

For  years  the  motors  performed  their  work  in  a  reliable 
and  satisfactory  manner.  An  exceptional  rain  occurred. 


CENTRIFUGAL  PUMPS  AND  EJECTORS      41 

The  streets  for  some  hours  were  submerged  with  flood 
water.  It  was  found  necessary  to  bring  the  entire  in- 
stallation into  service  at  the  shortest  possible  notice. 
Water  poured  through  the  ejector-station  covers,  but 
the  machinery  continued  to  work,  though  half  sub- 
merged, till  the  streets  were  drained. 

The  power  house  is  a  costly  brick  structure  with  gabled 
tiled  roof.  And  the  unusual  downpour  was  the  cause  of 
some  slight  leakage,  through  the  tiling.  A  few  drops  of 
water  fell  on  one  of  the  air-pump  motors.  The  arma- 
ture was  immediately  destroyed  and  the  condensing 
plant  put  out  of  action,  so  the  main  engines  had  to 
exhaust  to  atmosphere.  The  storm -water  motor  pump 
was  started,  but  after  running  a  couple  of  hours  the 
current  failed,  and  it  was  found  that  the  underground 
street  cable  had  perished  from  being  submerged  and 
injured  by  subsidence.  It  is  obvious  that  if,  in  place 
of  ejectors  operated  by  compressed  air,  motor  pumps 
had  been  erected  in  the  underground  chambers  or  wells 
below  the  streets,  they  would  have  been  put  out  of 
action  in  the  first  hour,  and  the  whole  drainage  system 
would  have  been  brought  to  a  standstill. 

REFUSE  IN  SEWAGE. 

When  unusual  floods  occur  in  large  cities,  immense 
quantities  of  refuse  and  mud  are  swept  into  the  sewers, 
and  if  screens  are  used  in  sumps,  they  rapidly  become 
blocked  and  the  turbid  mass  surges  over  the  top,  carry- 
ing all  before  it  into  the  pump  suction,  which  may  be 
completely  choked. 

In  nine  cases  out  of  ten  the  most  economical  and 
satisfactory  machinery  for  raising  sewage  is  the  simplest 
and  most  reliable,  and  the  motive  power,  if  converted 
into  a  secondary  power  and  distributed  over  large  areas, 


42     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

should  be  applied  as  directly  as  possible  to  the  work 
to  be  done,  without  the  interposition  of  mechanical 
devices,  and  no  corrosive  surfaces  or  working  parts 
should  be  brought  into  direct  contact  with  an  erosive 
fluid  if  it  can  possibly  be  avoided.  The  true  sewage 
pump  or  apparatus,  it  must  be  remembered,  should  be 
able  to  raise  and  discharge  a  liquid  or  viscous  fluid 
containing  every  conceivable  substance  and  variety  of 
refuse  which  may  cause  obstruction  or  destruction  to 
machinery. 

Like  marine  engines,  all  classes  of  sewage -raising 
apparatus  can  only  be  effectually  tested  in  actual  work 
over  long  periods. 


CHAPTER  III 

MECHANICAL  EFFICIENCY  OF  PUMPS  AND 
EJECTORS 

MECHANICAL  EFFICIENCY. 

FROM  the  foregoing  chapter  the  importance  of  knowing 
the  conditions  under  which  a  pump  or  ejector  is  working 
before  drawing  comparisons  will  be  understood. 

We  will  now  examine  the  mechanical  efficiency  of  the 
three  pumps  and  multiple  ejector  system  shown  on  the 
diagram,  Plate  XI.  To  ascertain  the  efficiencies  it  is 
necessary  to  determine  the  percentage  of  the  power 
developed  by  the  engine  or  motor  that  is  actually  con- 
verted into  useful  work.  This  is  accomplished  by  divid- 
ing the  pump  horse-power  by  the  indicated  horse- 
power— in  other  words,  the  work  done  by  the  power 
employed  to  do  it.  The  essential  facts  which  must  be 
determined  to  obtain  accurate  results  are  : 

1.  The  indicated  horse-power. 

This  presents  no  difficulties,  and  the  usual 
methods  employed  are  not  open  to  question, 
therefore  the  details  will  not  be  dealt  with  here. 

2.  The  pump  horse -power. 

That  is  the  weight  of  water  in  pounds  lifted  per 
minute,  multiplied  by  the  height  in  feet  to  which 
the  water  is  lifted,  including  frictional  head  divided 
by  33,000. 


MECHANICAL  EFFICIENCY  45 

In  each  case  these  pumps  and  ejectors  are  good  examples 
of  the  type  they  represent.  They  are  designed  and 
manufactured  by  well-known  makers  ;  but  it  is  as  well 
to  withhold  their  names,  as  there  is  no  desire  to  adver- 
tise one  or  penalise  another. 

They  all  discharge  an  effluent  from  the  same  source, 
and  it  would  be  difficult  to  find  a  more  suitable  instance 
for  comparison. 

EFFICIENCY  DIAGRAM. 

The  diagram,  Plate  XI.,  shows  at  a  glance  the  initial 
mean  efficiency  when  the  apparatus  was  first  installed 
and  after  twelve  months'  use. 

The  following  particulars  should  be  noted.  A  and  B 
both  draw  from  the  same  sump.  The  effluent  is  gritty, 
heavily  charged  with  refuse,  and  has  at  times  almost 
the  consistency  of  sludge  from  a  settling  tank. 

The  suction  for  A  has  a  drop  of  15  ft.  and  an  8-in. 
delivery  main  2f  miles  in  length.  It  is  a  three-throw 
single-acting  ram  pump,  with  a  speed  of  36  revolutions 
per  minute,  driven  by  a  single -phase  motor.  It  is  fitted 
with  multiple  clear-way  pump  valves,  and  has  a  rated 
capacity  of  500  gallons  per  minute. 

B  has  a  head  on  the  suction  and  discharges  through 
a  24-in.  main  1J  miles  in  length.  It  is  driven  by  a 
direct-coupled  motor  with  a  vertical  shaft  and  has  a 
speed  of  385  revolutions  per  minute. 

C  is  for  raising  sludge  from  settling  tanks.  There  is 
a  head  on  the  suction,  and  it  discharges  through  an 
8-in.  main  130  yards  in  length,  and  has  a  speed  of  1025 
revolutions  per  minute. 

D.  The  complete  installation  consists  of  130  ejectors 
divided  into  64  stations,  with  23  miles  of  sealed-sewage 
rising  mains  and  28  miles  of  compressed-air  mains  ; 


46     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

but  the  power  and  number  of  those  included  in  the 
tests  will  be  given  in  full  hereafter. 

CALIBRATING  DISCHARGE. 

In  order  to  calculate  these  efficiencies  it  was  necessary 
to  ascertain  the  volume  discharged. 

In  the  case  of  the  12  in.  X 12  in.  pump  (4)  it  was 
checked  in  the  following  manner. 

A  suitable  masonry  tank  was  built  at  the  outfall.  The 
main  discharged  into  one  end  and  the  water  escaped 
through  a  9-in.  pipe  at  the  other.  To  measure  the  water 
the  outlet  was  suddenly  closed,  the  level  of  the  water 
carefully  recorded,  and  the  time  noted  with  a  stop 
watch.  When  the  water  had  risen  to  a  predetermined 
level,  the  time  was  again  taken.  By  taking  the  area 
of  the  tank  and  the  height  the  water  rose,  it  was  possible 
to  calculate  the  rate  of  discharge  per  minute  of  the  pump. 
This  test  was  repeated  several  times,  with  a  difference 
of  1  or  2  per  cent.  only. 

The  discharge  from  the  14-in.  pump  (B)  was  deter- 
mined from  the  rate  the  water  was  lowered  in  the  suction 
well.  As  this  pump  drew  water  from  the  same  sump  as 
Ay  it  was  a  simple  matter  to  compare  the  time  taken  to 
lower  the  water  from  one  level  to  another,  by  the  two 
pumps.  The  initial  efficiency  of  the  6-in.  pump  (C) 
was  supplied  by  the  contractor,  and  the  ultimate  effi- 
ciency, when  after  a  year's  work  the  pump  practically 
ceased  to  discharge  and  was  dismantled. 

The  method  of  ascertaining  the  discharge  of  the 
ejectors  (D)  is  given  in  detail  below. 

EJECTORS:  CAPACITY  AND  DISCHARGE. 

The  capacity  of  a  pump  can  be  determined  from  the 
volume  of  water  displaced  by  the  ram  or  plunger  at 


MECHANICAL  EFFICIENCY  47 

each  revolution.  A  meter  can  also  be  utilised  for  the 
purpose,  but  the  extra  expense  is  seldom  incurred  in  a 
sewage  installation. 

However,  there  is  no  difficulty  in  shop  tests  and  on 
official  trials  in  determining  the  volume  discharged  with 
sufficient  accuracy  for  all  practical  purposes  ;  but  the 
pneumatic  ejector  is  on  a  different  footing. 

What  is  the  capacity  of  an  ejector  ? 

There  is  no  ram  or  plunger  from  which  to  calculate 
the  volume  of  the  liquid  displaced,  but  a  highly  com- 
pressible fluid,  subject  to  variation  in  volume  according 
to  pressure.  Let  us  assume  an  ejector  is  rated  at  50 
gallons.  That  is  to  say,  it  should  discharge  50  gallons 
from  the  time  the  compressed  air  is  admitted  till  the 
exhaust  opens.  The  question  is,  under  working  condi- 
tions, Is  the  discharge  uniform  ?  Is  it  more  ?  Is  it  less  ? 

Authorities  do  not  agree  on  this  vital  subject.  Hence 
the  efficiency  of  the  ejector  is  often  a  matter  of  contro- 
versy. 

One  authority  questions  the  propriety  of  calculating 
the  sewage  discharged,  when  taken  as  the  product  of 
the  ejector  capacity  in  gallons.  On  the  other  hand, 
another  authority  considers  that  it  is  difficult  to  get 
anything  more  exact  for  measuring  a  volume  of  water ; 
while  a  third  authority  calibrated  a  50-gallon  ejector 
and  obtained  a  discharge  of  38  gallons  ! 

In  view  of  such  conflicting  opinions,  the  author  makes 
no  apology  for  giving  concise  details  as  to  how  the 
capacity  and  discharge  of  the  ejectors  was  determined 
for  the  efficiencies  shown  on  the  diagrams. 

CALIBRATING  EJECTORS. 

There  are  three  methods  of  calibrating  the  discharge 
of  ejectors : 


48     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

1.  By  calculating  from  the  interior  measurements  the 

capacity  of  the  ejector  body. 

2.  By  weighing  the  actual  volume  of  liquid  expelled 

at  each  stroke. 

3.  By  passing  the  discharge  through  a  water  meter 

of  suitable  design. 

Obviously  if  it  is  possible  to  pass  the  sewage  through 
a  meter  of  known  accuracy,  the  result  from  1  and  2 
is  immaterial.  But  as  far  as  the  author  is  aware, 
there  is  no  instance  on  record  where  such  means  have 
been  available.  The  figures  now  given  are  compiled 
from  investigations  carried  out  over  several  years  from 
time  to  time  as  opportunity  offered.  The  design  and 
size  of  the  ejectors  now  given  correspond  with  those 
shown  on  Plate  IX. 


MECHANICAL  EFFICIENCY 


49 


DISCHARGE  TABLE 
Capacity  and  Discharge  of  Ejectors 


Index 
Letter. 

Size, 
Galls. 

Particulars. 

Cubic 
Feet. 

Gallons. 

Excess 
per 
Cent. 

A 

500 

From    the    internal 

diameter    of    the 

spherical  body,  not 

including  base      .         87*11 

540-56 

8-11 

B 

300 

From  interior  meas- 

urements at  water 

level  after  discharg- 

ing and  filling 

55-65 

347-25 

15-75 

C 

250 

From    the    internal 

i. 

diameter    of    the 

spherical  body  not 

including  base  or 

float  chamber      » 

44-60 

275-30 

10-12 

D 

150 

Do.            do. 

28-73 

176-30 

17-53 

E 

100 

Do.            do. 

18-81 

114-37 

14-37 

F 

50 

From  interior  meas- 

urements with  al- 

lowance  for   base 

and  float  chamber 

9-81 

58-25 

16-50 

G 

500 

By  weight  of  water 

expelled  from  three 

discharges   plus   1 

per  cent,  for  leak- 

Kilos. 

age  and  error 

2291-57 

505-06 

1-01 

H 

250 

Do.            do. 

1155-53 

254-68 

1-87 

J 

50 

Do.            do. 

251-40 

55-41 

10-82 

Note. — In  the  case  of  A,  (7,  D,  E,  F,  three  gallons  have  been  deducted 
to  allow  for  the  internal  weight. 

From  these  figures  it  does  not  appear  that  the  various 
sizes  are  made  with  a  uniform  margin  for  possible  loss 
or  excess  discharge  on  the  rated  capacity.  In  case  B 
the  capacity  was  gauged  as  follows,  and  it  will  be  noted 

D 


50     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

from  the  design,  Plate  IX.,  that  it  is  the  only  size  of 
those  given  in  which  such  a  method  can  be  adopted. 

CALIBRATING  EJECTORS  BY  MEASUREMENT. 

The  ejector  was  under  ordinary  working  conditions. 
Immediately  after  a  discharge  the  delivery  sluice  valve 
was  closed.  The  cover  was  then  prepared  for  rapid 
removal  by  unscrewing  the  nuts.  As  the  ejector  filled, 
the  air  stop  valve  was  closed,  and  the  inlet  sluice  valve 
was  screwed  down  till  half  a  turn  open.  Immediately 
the  float  rose  the  inlet  sluice  valve  was  closed,  the  cover 
removed,  and  the  height  of  the  water  measured.  The 
cover  was  then  replaced,  the  delivery  sluice  valve  opened 
and  the  ejector  discharged,  and  the  valve  again  closed. 
Finally,  the  cover  was  removed  and  the  level  to  which 
the  water  had  fallen  was  measured. 

In  daily  automatic  working  the  sluice  valves  are 
always  fully  open,  and,  provided  the  fellow  ejector  is 
still  discharging,  the  water  continues  to  rise,  because  the 
filling  of  the  ejector  is  stopped  by  the  admission  of  the 
compressed  air  and  not  by  the  float  rising.  It  must  be 
remembered  the  ejectors  can  fill  together,  but  they 
cannot  discharge  together. 

It  is  obvious  the  discharge  can  vary  from  this  cause 
alone.  Again  there  is  an  appreciable  pause  between 
the  rising  of  the  float  and  the  pressure  of  the  air  on  the 
liquid,  even  with  a  single  ejector  working.  Also  when 
the  ejectors  discharge  through  long  mains,  the  kinetic 
energy  of  the  water  tends  to  over  discharge.  On  the 
other  hand,  in  course  of  time  fouling  of  the  ejector  body 
and  floating  matter  tend  to  lessen  the  discharge. 

CALIBRATING  EJECTORS  BY  WEIGHT  OF  WATER  EXPELLED. 
There  is  no  more  accurate  method  of  calibrating  the 


MECHANICAL  EFFICIENCY  51 

contents  of  an  irregular  vessel  than  by  the  weight  of  the 
liquid  it  contains.  But  the  difficulty  of  reproducing 
working  conditions,  automatic  actions,  and  detecting 
leakage,  leave  a  degree  of  uncertainty  attached  to  the 
operation  in  some  instances. 

The  method  adopted  in  the  case  of  6r,  H,  J  was  as 
follows. 

The  delivery  sluice  valve  on  the  rising  main,  some  30 
ft.  from  the  ejector,  was  closed  and  the  reflux  valve  cover 
fitted  with  a  2-in.  W.I.  pipe.  A  50-gallon  tank  was 
then  placed  on  a  portable  weighing  machine  and  arranged 
so  that  the  water  could  be  drawn  off  from  the  ejector 
directly  into  the  tank  and  weighed. 

In  the  case  of  the  50-gallon  ejector  (J)  this  was  done 
in  a  minute  or  so,  and  the  loss  must  have  been  insig- 
nificant ;  but  with  the  500-gallon  ejectors  (G)  the  opera- 
tion took  from  twenty  to  thirty  minutes,  and  it  is  at 
once  apparent  that  though  the  loss  in  J  approximated 
to  working  conditions  the  loss  in  G,  that  is,  the  percentage 
of  water  that  failed  to  reach  the  tank  would  be  unduly 
magnified.  It  must  be  borne  in  mind  that  in  ordinary 
working  conditions  both  these  ejectors  discharge  in 
half  a  minute,  and  there  is  no  reason  to  assume  that  the 
slip  in  one  is  greater  than  the  slip  in  the  other. 

In  the  case  of  these  ejectors  a  certain  number  dis- 
charged through  a  33-in.  Venturi  meter,  thus  affording 
a  unique  opportunity  for  checking  the  discharge  under 
actual  working  conditions  over  prolonged  periods. 

EJECTOR  DISCHARGE  COMPARED  WITH  VENTURI  METER. 

The  Venturi  meter  is  a  well-known  standard  instru- 
ment of  accepted  accuracy,  and  the  only  type,  by  reason 
of  the  absence  of  working  parts,  through  which  crude 
sewage  can  be  measured  with  success. 


52     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

The  following  table  is  of  singular  interest. 

Ejector  and  Venturi  Meter  Discharge  in  Cubic  Metres 


Time. 

No. 
of 
Ejec- 
tors. 

Capacity. 
Gallons. 

Discharge. 
Cubic 
Metres. 

Ejector. 
Total. 
Cubic 
Metres. 

Venturi. 
Cubic 
Metres. 

Ex- 
cess 
per 
Cent. 

12  hours 

10 

500 

5,738 

2 

250 

550 

2 

50 

270 

6,558 

6,870 

4-37 

24     „ 

10 

500 

10,857 

4 

250 

806 

4 

100 

592 

4 

50 

37 

12,292 

12,900 

4-70 

24     „ 

5 

500 

6,024 

2 

250 

476 

;  . 

2 

100 

19 

! 

1 

50 

8 

6527  !      6,939 

5-94 

31  days 

36 

500  to  50 

529,760 

554,800 

4-51 

It  will  be  observed  that  this  table  practically  amounts 
to  a  comparison  between  the  Venturi  meter  and  the 
500-gallon  ejector  owing  to  the  insignificant  contribu- 
tion from  the  smaller  sizes.  It  is  interesting  to  com- 
pare these  figures  with  the  measurements  by  weight, 
and  it  will  be  seen  that  the  suggestion  put  forward  to 
account  for  the  difference  in  margin  between  the  50 
and  500  gallon  ejectors  is  not  without  foundation. 
These  figures  show  that  the  ejectors  in  actual  work 
discharge  more  than  their  rated  capacity  according  to 
the  volume  registered  by  the  Venturi  meter. 

CHEMICAL  TEST  OF  VENTURI  METER. 

The  following  figures  show  the  results  of  a  chemical 
test  by  qualified  officials,  of  the  rate  of  flow  immediately 
above  the  meter : 


MECHANICAL  EFFICIENCY  53 

Venturi  Meter.  Chemical  Test.  Excess. 

694  cub.  metres  705  cub.  metres         1*6  per  cent, 

per  hour.  per  hour. 

That  is  to  say,  the  rate  of  flow  registered  by  the  meter 
was  lower  than  that  recorded  by  the  chemical  test.  For 
the  efficiency  trials  the  ejector  discharge  was  taken  at 
4-75  per  cent,  in  excess  of  the  rated  capacity,  and  sub- 
sequent records  show  that  this  is  Etot  excessive. 

PRESSURE  GAUGE  ERRORS. 

The  height  to  which  the  weight  of  water  is  lifted — in 
other  words,  the  '  working  head,'  including  friction  in 
the  mains — is  determined  by  the  pressure  recorded  on 
the  gauge  attached  to  the  ejector  body.  Few  gauges  are 
precisely  accurate,  and  at  working  pressures  of  100 
and  200  Ibs.  per  sq.  inch  a  slight  error  is  of  little  con- 
sequence ;  but  with  pressures  that  range  from  10  to  25 
Ibs.  per  sq.  inch,  a  small  error  is  often  equal  to  8  per 
cent,  or  10  per  cent. 

The  ordinary  Bourdon  gauge  is  a  simple  apparatus, 
and  if  accuracy  is  desired  it  is  imperative  to  adjust 
each  gauge  before  use  by  means  of  a  testing  machine. 
The  Crosby  tester  is  a  standard  dead-weight  apparatus, 
and  the  following  table  shows  the  error  of  each  gauge 
tested  by  a  machine  of  this  type : 


54     EFFICIENCY  OF  PUMPS  AND  EJECTORS 


Error  of  Gauge  at  Mean  Working  Pressure 
Ibs.  per  Sq.  Inch 


Ejector 
Station. 

Near  Side. 

Off  Side. 

Ejector 
Station. 

Near  Side. 

Off  Side. 

32 

-0-50 

-1-25 

33 

-1-00 

-1-00 

54 

-1-50 

-1-25 

27 

-1-00 

-2-00 

25 

-1-50 

5 

-1-00 

25S.W.D. 

-1-00 

-6-75 

15 

-1-00 

55 

-2-25 

-1-50 

26 

-1-50 

-i-oo 

31 

-1-25 

-1-00 

75 

60 

i  /..    . 

-1-00 

71 

-1-50 

-6-50 

65 

-0-75 

-1-00 

2 

-0-75 

-1-00 

67 

-0-25 

23 

+0-25 

58 

-1-00 

-1-50 

23^4 

-1-00 

-2-25 

57 

-1-50 

-1-50 

235 

-1-25 

-1-00 

37 

-2-50 

•  • 

It  will  be  noticed  of  these  46  gauges  36  register  at 
too  low  a  figure,  9  are  correct,  and  1  is  too  high.  It 
will  be  readily  understood  from  the  above  table  that 
in  calculating  the  work  done  by  a  series  of  small  engines, 
distributed  over  a  wide  area,  that  inaccurate  records 
will  in  the  aggregate  amount  to  a  serious  error,  and  the 
importance  of  correct  facts  cannot  be  overestimated. 


Am  MAINS:  PROPORTIONAL  Loss. 

In  an  ejector  system,  especially  of  great  extent,  the 
leakage  from  the  air  mains  is  the  same  whether  a  full- 
power  trial  or  only  one -sixth  of  a  full-power  trial  is 
run.  Hence  it  follows  that  to  arrive  at  the  correct 
efficiency  of  a  system,  a  proportion  of  the  air-main  losses 
must  be  deducted  according  to  the  power  developed. 


MECHANICAL  EFFICIENCY  55 

The  following  table  shows  a  series  of  air-main  tests  : 

AIB-MAIN  TESTS 


I 

T 

Juoss  in 

Revs. 

No. 

Date. 

Press, 
in  Ibs. 

hour. 
TA™ 

Loss  per 
Cent. 

p.m.  to 
make 

JUUVc 

good. 

.A 

May    4,  1915     . 

50-00 

5-00 

10-00 

B       May    3,  1916     . 

23-50 

3-50 

14-80 

9-50 

C 

Aug.  10      „ 

23-50 

4-00 

17-00 

11-70 

D 

Dec.    4      „ 

24-00 

6-50 

27-00 

18-07 

E 

Jan.  23,  1917     . 

24-00 

4-50 

18-75 

12-53 

F 

Feb.    3      „        . 

22-50 

4-00 

17-70 

10-90 

With  the  exception  of  test  A,  none  of  these  results 
are  good,  as  little  recaulking  had  been  done.  There  is 
no  difficulty  at  these  low  pressures  in  maintaining  the  air 
mains  sufficiently  tight  for  an  ejector  efficiency  of  40  per 
cent.,  and  without  doubt  it  pays  to  reduce  leakage  to 
5  per  cent,  or  6  per  cent. 


AIR-MAIN  TESTING. 

To  determine  the  amount  of  leakage  from  the  air 
mains,  all  the  ejectors  are  stopped.  The  compressing 
engines  are  then  stopped  and  the  pressure  recorded. 
When  the  pressure  has  fallen  to  a  predetermined  figure, 
the  engine  is  restarted.  By  recording  the  number  of 
revolutions  taken  to  make  good  the  lost  pressure,  and 
dividing  the  total  by  the  duration  of  the  test  in  minutes, 
the  I.H.P.  absorbed  by  leakage  can  be  determined. 
It  must  not  be  overlooked  that  the  compressed  air  is 
simply  a  method  of  transmission  of  the  power  employed 
to  do  the  work. 


56    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

EJECTOR  TRIALS  :  CONDITIONS. 

It  is  manifest  that  owing  to  the  nature  of  the  working 
fluid,  an  ejector  system,  to  give  the  best  results,  must 
be  run  with  a  minimum  air  pressure  and  a  maximum 
volume  of  water  —  conditions  which  it  is  practically 
impossible  to  obtain  in  a  multiple -ejector  system  on 
first  being  installed.  With  a  single -pumping  installa- 
tion it  is  easy  enough  to  by-pass  the  liquid  to  the  sump 
for  trial  purposes. 

EJECTOR  EFFICIENCY  DIAGRAM. 

Plate  XII.  shows  graphically  how  an  ejector  system 
maintains  efficiency.  The  first  and  second  results  are 
12-hour  trials,  the  next  two  24-hour  trials,  and  the  last 
two  over  periods  of  four  weeks  each.  It  is  these  last 
two  trials  that  are  of  special  interest,  not  only  from  the 
long  period  over  which  they  are  taken,  but  owing  to  the 
huge  volume  of  water  raised  and  the  large  number  of 
ejectors  included.  To  ensure  the  existence  of  ordinary 
working  conditions,  no  intimation  was  given  to  the  daily 
inspection  staff,  but  frequent  checking  to  see  that  the 
ejector  counters  were  in  good  order.  The  details  of  the 
ejector  powers  for  the  October  test  were  49  ejector 
stations,  containing  100  ejectors. 

EJECTOR  EFFICIENCY  TRIAL. 

May  10,  1916,  6  A.M.  to  6  P.M. — 12  hours 

No.  3  engine  I.H.P.  110'21  Vacuum     .         .  27'6 

Steam  pressure  .  154' 10  Air  pressure         .  20'9 

Revs,  per  minute  .  84- 69  Steam  per  I.H.P. 

Steam  temperature  .  477*20  per  hour          .  15*9 

Fifteen  ejector  stations  were  included  in  this  trial. 


MECHANICAL  EFFICIENCY 


57 


EJECTOR  RESULTS 


No.  of 
Ejector. 

Capacity. 
Gallons. 

Revolu- 
tions. 

Gallons 
discharged. 

Head  in 
Feet. 

Pump 
Horse- 
power. 

32 

500 

387 

193,500 

40-54 

3-301 

54 

500 

1,033 

516,500 

47-42 

10-308 

25 

500 

863 

431,500 

42-15 

7-654 

25S.W.D. 

500 

200 

100,000 

42-15 

1-773 

55 

250 

681 

170,250 

30-53 

2-187 

31 

500 

276 

138,000 

32-38 

1-907 

60 

50 

1,542 

77,100 

36-03 

1-184 

37 

100 

854 

85,400 

30-49 

1-095 

33 

300 

360 

108,000 

44-69 

2-031 

27 

100 

1,085 

108,500 

43-26 

1-975 

5 

500 

253 

126,500 

46-10 

2-454 

15 

250 

301 

75,250 

39-15 

1-239 

75            150 

79 

11,850 

43-89 

0-218 

23 

250 

226 

56,500 

41-62 

0-989 

23B 

100 

202 

20,200 

38-62 

0-328 

2,219,050 

38-643 

Venturi  meter  correction  =4-75  per  cent. 

Therefore  P.H.P.  =40-478. 

Difference  of  pressure  of  1  Ib.  in  receiver 

=0-30  I.H.P. 

Therefore  I.H.P.  =109-91. 

40*4-78 
Overall  efficiency,  including  all  mains =^±r_±AT=36« 828. 


Two-thirds  of  air-main  leakage 

Therefore  efficiency  with  propor- 
tional loss 


109-91 
=8-847  I.H.P 


40-478 
101-063 


=40-052. 


en 


CO 


O) 


3  . 

O)  eo 


? 


8 


MECHANICAL  EFFICIENCY 


59 


EJECTOB  EFFICIENCY  TRIALS  :  TWELVE  HOURS . 

Here  is  the   result   of  an  efficiency  trial,   including 
14  stations  for  12  hoars  : 

August  7,  1916,  6  A.M.  to  6  P.M. 

No.  3  engine  I.H.P.   .    119-11     Vacuum     .         .         .    26-0 

Steam  pressure       •    .    145-3      Air  press,  at  receiver     20-70 

Revs,  per  minute       .      83-5       Steam  temperature     .  480-8 

Steam  per  I.H.P.  per  hour,  15-32  Ibs. 

Ejector  Pump  Horse-powet  s 


No.  of 
Ejector. 

Capacity. 
Gallons. 

Revolu- 
tions. 

Gallons 
discharged. 

Head  in 

Feet. 

Pump 
Horse- 
power. 

32 

500 

365 

182,500 

40-70 

3-126 

54 

500 

780 

390,000 

30-26 

4-966 

25 

500 

962 

481,000 

38-78 

7-850 

25S.WD. 

500 

185 

92,500 

24-27 

0-944 

55 

250 

485 

121,250 

27-83 

1-420 

31            500 

238 

119,000 

32-82 

1-643 

60 

50 

1,193 

59,550 

37-30 

0-936 

33 

300 

405 

121,500 

46-10 

2-357 

27 

100 

1,362 

136,200 

34-18 

1-959 

5            500 

578 

289,000 

42-73 

5-197 

15            250 

286 

71,500 

37-42 

1-126 

26 

250 

249 

62,250 

43-42 

1-137 

75            150 

95 

14,250 

45-41 

0-272 

23 

250 

490 

132,500 

43-58 

2-246 

2,263,100 

35-179 

Venturi  meter  correction  =  4-75  per  cent. 

Therefore  P.H.P.  =36-850. 

36*850 

Overall  efficiency,  including  all  mains= —  — =30-537. 

119*110 

Two-thirds  of  air-main  leakage  =12*51  I.H.P. 

Therefore  efficiency  with  proper- 

tionalloss  =i06^6T=3 


60     EFFICIENCY  OF  PUMPS  AND  EJECTORS 


EJECTOR  EFFICIENCY  TRIAL 
October  1  to  October  31,  1917 


No.  1  and  2  engines 

I.H.P.       ./       .     214-82 
Revs,  per  minute  .     150-22 


Steam  pressure  . 
Vacuum 


160  Ibs. 
22  inches 


No.  of 
Ejector. 

Capa- 
city. 

Revolu- 
tions. 

Gallons  dis- 
charged. 

Head  in 

Feet. 

Pump 
Horse- 
power. 

32 

500 

30,473 

15,236,500 

43-89 

4-540 

54 

500 

23,914 

11,957,000 

46-20 

3-749 

25 

500 

65,539 

32,769,500 

46-20 

10-278 

25S.W.D. 

500 

53,987 

26,993,500 

34-65 

6-350 

55 

250 

24,048 

6,012,000 

32-34 

1-320 

31 

500 

11,261 

5,630,500 

32-34 

1-237 

60 

50 

68,145 

3,407,250 

48-51 

1-122 

65 

250 

37,460 

9,365,000 

39-27 

2-497 

67 

50 

95,008 

4,750,400 

43-89 

1-416 

58 

100 

58,505 

5,850,500 

46-20 

1-835 

69 

150 

59,985 

8,997,750 

46-20 

2-822 

57 

100 

7,211 

721,100 

39-27 

0-193 

59 

250 

26,408 

6,602,000 

43-89 

1-966 

53 

250 

4,817 

1,204,250 

43-89 

0-352 

68 

250 

24,545 

6,136,250 

48-51 

2-020 

63 

100 

3,205 

320,500 

46-20 

0-100 

61 

100 

6,544 

654,400 

46-20 

0-206 

62 

100 

42,174 

4,217,400 

46-20 

1-323 

37 

100 

9,838 

983,800 

32-34 

0-216 

33 

300 

42,107 

12,632,100 

48-51 

4-160 

27 

100 

32,923 

3,292,300 

39-27 

0-878 

5 

500 

17,210 

8,605,000 

48-51 

2-834 

14 

250 

41,657 

10,414,250 

50-82 

3-592 

15 

250 

11,142 

2,785,500 

48-51 

0-917 

22 

150 

193 

28,950 

48-51 

0-010 

17 

100 

1,163 

116,300 

41-58 

0-033 

26 

250 

11,855 

2,963,750 

46-20 

0-930 

39 

100 

8,149 

814,900 

43-89 

0-243 

30 

150 

1,521 

228,150 

41-58 

0-007 

28 

100 

4,408 

440,800 

43-89 

0-014 

6 

150 

34 

5,100 

46-20 

0-002 

51 

500 

9,825 

4,912,500 

46-20 

1-540 

MECHANICAL  EFFICIENCY 


61 


EJECTOR  EFFICIENCY  TRIAL  (continued) 
October  1  to  October  31,  1917 


No.  1  and  2  engines 

I.H.R  .     214-82 

Revs,  per  minute  .     150*22 


Steam  pressure  .     160  Ibs. 
Vacuum  22  inches 


No.  of 
Ejector. 

Capa- 
city. 

Revolu- 
tions. 

Gallons  dis- 
charged. 

Head  in 
Feet. 

Pump 
Horse- 
power. 

18 

250 

17 

4,250 

43-89 

0-002 

66 

150 

61 

9,150 

41-58 

0-003 

56 

500 

10,262 

5,131,000 

46-20 

1-610 

75 

150 

7,139 

1,070,850 

32-34 

0-236 

71 

250 

2,171 

542,750 

43-89 

0-162 

72 

250 

612 

153,000 

43-89 

0-046 

23 

250 

40,748 

10,187,000 

46-20 

3-195 

23.4 

250 

3,263 

815,750 

46-20 

0-256 

235 

100 

75,594 

7,559,400 

46-20 

2-370 

1 

50 

813 

40,650 

43-89 

0-122 

2 

50 

31,279 

1,563,950 

43-89 

0-466 

3 

50 

22,586 

1,129,300 

43-89 

0-337 

12 

100 

310 

3,100 

41-58 

0-009 

4 

50 

14 

700 

41  -58\ 

73 

250 

6 

1,500 

,  , 

24 

150 

9 

1,350 

46-20  i 

o-ooi 

41 

50 

4 

200 

64 

150 

•• 

.  .   ) 

227,291,000 

68-717 

Venturi  meter  correction 
Therefore  P.H.P. 


=4-75  per  cent. 
=71-981. 


Overall  efficiency,  including  all  mains = 

One-third  of  air-main  leakage 
Three  ejector  blow-throughs 

Therefore  efficiency  with  propor- 
tional loss 


71-981 


33-506. 


214-824 

15-037  I.H.P. 

0-863  I.H.P. 


71-981 
198-922 


=36-185. 


62     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

EJECTOR  TRIAL:  REMARKS. 

The  pump  horse -powers  given  leave  little  room  for 
question,  neither  is  the  indicated  horse -power  open  to 
much  doubt ;  but  there  are  losses  detrimental  to  the  best 
efficiency  which  can  only  be  enumerated  and  not  calcu- 
lated. And  it  may  be  stated  definitely  that  the  true 
efficiency  is  considerably  higher,  probably  reaching 
40  per  cent.  If  only  such  favourable  conditions  were 
permitted,  as  invariably  exist  on  pumping -engine  trials, 
there  is  no  reason  why  even  higher  figures  should  not 
be  obtained.  However,  it  is  preferable  to  give  actual 
results  than  figures  based  on  assumption. 

From  recorded  tests  the  estimated  air-main  loss  was 
not  less  than  21  per  cent.  A  considerable  volume  of 
air  was  used  for  auxiliary  purposes.  There  was  also 
loss  in  changing  engines,  and  on  numerous  occasions 
during  the  month  the  engines  were  overtaxed,  and 
two  forced  stoppages  took  place.  The  circulating  water 
for  the  condenser  was  inadequate  and  often  112°  F. ; 
also  many  other  minor  faults  existed  which  would  not 
be  tolerated  on  an  official  trial. 

EJECTOR  AND  PUMP  TRIAL  COMPARED. 

The  feature  of  the  above  trial  is  the  immense  number 
of  small  powers,  and  that  two -thirds  of  full  power  was 
employed  continually  over  so  long  a  period  under  ordinary 
conditions.  If  pumps  were  substituted  for  ejectors 
under  such  conditions,  friction  would  absorb  nearly  the 
whole  power,  yet  it  is  often  the  practice  to  compare 
the  efficiency  of  such  an  ejector  installation  with  that 
of  a  single-pumping  plant  of  equal  horse-power. 

It  is  manifest  a  single  large  power  must  give  the  higher 


MECHANICAL  EFFICIENCY 


63 


mechanical  efficiency,  especially  when  every  favourable 
condition  can  be  provided. 

The  reciprocating  ram  pump  has  been  brought  to  an 
extraordinary  degree  of  perfection,  and  in  order  to 
illustrate  the  immense  difference  which  still  exists  in 
mechanical  efficiency  between  such  a  pump  and  an 
ejector  system  even  after  making  every  allowance,  the 
results  of  two  trials  are  given  below. 

The  engine  was  of  the  quadruple  expansion  type,  steam 
cylinders,  17  ins.  x  27  ins.  X  33  ins.  X  49  ins.  with  crank 
and  flywheel,  coupled  direct  to  a  three-throw  single-acting 
ram  pump,  21 J  ins.  x3  ft. 

Reciprocating  Pump  Trial 

Trial.  A  B 

Duration  of  trial     ;.  ,^,  12  hours.  23- 75  hours. 

Revolutions  per  minute  .  23-42  23-5 

Total  head        .         .  .  144  ft.  183-73  ft. 

Steam  pressure          .  "•''.-•  198-01  Ibs.  200-00  Ibs, 

Steam  temperature    .  .  522°  F.  518°  F. 

Vacuum  .         .         .  ,;  25-82  23-37 

Steam  per  I.H.P.      *  <4  9-75  Ibs.  10-18  Ibs. 

Pump  horse-power    .  .  140-94  180-27 

Indicated  horse-power  v  155-08  195-4 

Mechanical  efficiency  .  90-88  92-8 

Gallons  raised  per  minute  .  3229-88  3240-8 

Total  in  gallons  raised  .  2,325,513  4,618,140 


The  pump  was  discharging  the  same  effluent  after 
screening  as  the  ejector.  In  considering  the  great 
difference  it  must  be  pointed  out  the  efficiency  of  the 
air -compressing  engines  was  very  much  less.  With 
an  efficiency  of  90,  which  the  leading  makers  guarantee 
at  the  present  day,  the  ejectors  would  not  fall  so  far 
behind  as  disclosed  by  these  tests. 


64     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

There  is  inevitable  loss  in  compressing  air,  but  at  the 
low  pressure  used  in  ejector  systems  this  does  not  amount 
to  a  serious  figure.  The  principal  cause  is  preventable 
leakage  and  the  type  of  compressing  machinery  installed. 

It  is  clear  an  ejector  system  cannot  attain  the  effi- 
ciency of  a  single  pumping  installation  ;  but  it  must  not 
be  supposed  that  92  per  cent,  is  maintained  in  daily 
practice.  Probably  the  efficiency  of  the  12  ins.  X 12  ins. 
(A)  pump  in  Plate  XI.  is  as  high  if  not  higher  than 
90  per  cent,  of  such  pumps  in  use  raising  crude  sewage. 

SUMMARY  OF  EFFICIENCIES. 

To  sum  up  :  the  high-class  reciprocating  pump  is  by 
far  the  most  mechanically  efficient  device  in  use. 

The  centrifugal  pump,  though  initially  efficient,  rapidly 
fails. 

The  pneumatic  ejector,  commencing  at  a  lower  effi- 
ciency, does  not  deteriorate. 

The  merits  of  one  system  compared  to  another  will 
always  be  a  matter  of  controversy.  Much  depends  upon 
the  point  of  view  from  which  they  are  considered.  But 
in  the  majority  of  sewage  undertakings  there  is  little 
doubt  which  is  the  best  method  to  adopt  from  the 
mechanical  standpoint,  if  the  evidence  and  observation 
here  set  out  are  carefully  weighed  and  analysed. 

It  cannot  be  too  emphatically  stated  that  it  is  the 
mechanical  efficiency  which  a  power  device  maintains, 
and  not  that  which  it  can  attain  when  first  installed, 
that  should  be  kept  in  view. 

There  is  no  class  of  machinery  in  which  an  official  trial 
is  apt  to  give  more  misleading  results,  than  that  employed 
in  raising  crude  sewage. 

Irrefutable  evidence,  based  on  long  periods  of  work- 
ing, should  alone  be  taken  as  conclusive. 


PLATE  XIII 


r 


CAIRO  MAIN  _DRAINAOE. 

QUADRUPLE  EXPANSION   ROTATIVE 
PUMPING     ENGINES . 


VERTICAL  STEAM  PUMPING  ENGINE 


CHAPTER  IV 
COMMERCIAL  EFFICIENCY 

To  compare  the  commercial  efficiency  of  a  pumping  plant 
to  an  ejector  system,  it  is  necessary  to  give  a  brief  descrip- 
tion of  what  they  consist.  We  have  to  consider  the 
capital  cost,  construction,  supervision,  and  maintenance. 
For  the  present,  only  the  essentials  will  be  taken  and 
the  results  analysed,  the  details  being  held  over  to  a 
later  chapter. 

PUMPING  INSTALLATION:  SUMMARY. 

A  large  pumping  installation  will  consist  of  four  or  five 
units  of  150  horse -power  apiece,  and  may  be  either 
direct-acting  or  rotary  crank  and  flywheel  engines, 
actuating  three-throw  single-acting  ram  pumps.  Such 
machinery  will  be  suitable  for  raising  eight  or  nine  million 
gallons  of  sewage  per  day  to  a  height  of  130  feet  to  200 
feet,  according  to  the  normal  or  maximum  volume 
passing  through  the  main. 

A  fine  example  of  a  large  vertical  steam  pumping 
engine  for  raising  crude  sewage  is  shown  in  Plate  XIII. 

This  is  a  quadruple  expansion  rotative  engine  with 
two  flywheels.  The  general  design  is  of  the  marine  type, 
with  an  open  front  and  massive  supporting  columns. 
The  engine  bed -plate  is  placed  on  the  same  level  as  the 
engine-house  floor,  and  there  are  three  stages,  one  above 
the  other,  to  gain  access  to  the  upper  part  of  the  engine. 

E  « 


66     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

There  are  four  steam  cylinders,  three  side  by  side  and 
the  fourth  in  line  above  the  centre  cylinder. 

It  will  be  observed  there  are  three  single-acting  pumps, 
and  the  left-hand  pump  shows  the  ram  at  the  top  of  its 
stroke.  Each  of  these  rams  is  directly  coupled  to  the 
piston-rod  cross  head.  The  cylinder  valves  are  operated 
by  bevel  gear  and  shafting  driven  from  the  main  crank 
shaft.  Such  engines  as  these  have  a  great  range  of  speed, 
and  will  run  with  a  fuel  consumption  of  only  ten  Ibs. 
of  steam  per  indicated  horse-power  per  hour. 

It  will  be  observed  the  foundations  consist  of  a  solid 
mass  of  concrete,  and  a  chamber  in  the  base  of  this  mass 
forms  the  suction  wells  from  which  the  pumps  draw. 

A  pumping  installation  may  be  divided  as  follows  : 

1.  Engine  and  boiler  house,  chimney  shaft. 

2.  The  pump  chambers  and  sump. 

3.  The  screening  chamber. 

4.  The  machinery,  engine  and  pumps. 

5.  The  rising  main. 

Assuming  the  engines  are  of  the  vertical  triple  expan- 
sion type,  the  bed-plate  will  be  at  floor  level,  the  head 
of  the  supporting  columns  the  first  stage,  and  a  second 
stage  for  access  to  the  top  of  the  engine.  As  head  room 
must  be  given  for  the  travelling  crane,  it  is  clear  that 
the  building  will  be  massive  and  of  great  height.  Below 
the  floor  the  condensers,  air  pumps,  and  feed  pumps  will 
be  arranged,  and  below  this  again  the  pump  floor,  in 
which  are  bedded  the  anchor  bolts.  In  nine  cases  out 
of  ten,  sewage  pumps  require  deep  foundations,  as  the 
sump  from  which  they  draw  the  effluent  must  be  below 
the  level  of  the  sewer  outfall,  and  the  suction  of  the 
pump  must  again  be  provided  with  some  depth  to  draw 
from. 


COMMERCIAL  EFFICIENCY  67 

SUMP. 

The  sump  or  suction  chamber  will  be  directly  below 
the  pumps,  and  as  the  whole  weight  of  the  engines  rest 
on  this  structure,  it  must  be  of  great  massiveness  and 
strength.  In  water-logged  ground  a  sump  of  this 
description  is  an  extremely  costly  part  of  the  work  to 
build,  and  will  often  absorb  the  greater  part  of  the 
building  estimates.  The  necessity  of  having  this  sump 
beneath  the  pumps  in  large  units  is  very  real,  as  the 
first  condition  to  successful  working  is  to  have  the  suction 
pipes  as  short  as  possible. 

SCREENING  CHAMBER. 

This  chamber  has  also  to  be  of  great  depth  and  in 
duplicate,  or  rather  bisected  by  a  wall,  so  one  half  can 
be  cleaned  while  the  other  is  in  use.  The  screens  them- 
selves are  provided  with  rakes  attached  to  endless  chains, 
for  cleaning  the  bars  of  refuse  and  raising  it  to  the  top, 
while  a  chain  of  dredging  buckets  has  also  to  be  provided 
for  raising  solids  from  the  bottom.  Such  machinery  is 
usually  run  by  motors,  and  a  building  must  be  erected 
to  cover  them.  Trolleys  and  rails  will  be  required  to 
remove  the  screenings  as  fast  as  they  are  raised.  The 
wear  and  tear  on  this  gear  is  extremely  severe,  but 
this  cannot  be  avoided.  This  section  is  indeed  costly 
to  build  and  costly  to  maintain. 

AUXILIARIES. 

An  ample  fresh-water  supply  must  be  arranged ;  pos- 
sibly a  well  has  to  be  sunk  and  a  cooling  pond  for  the 
condenser  circulating  water ;  engines  and  dynamos  for 
driving  the  motors  for  the  screening  chamber,  air  com- 
pressors for  filling  the  air  vessels  on  the  main  pumps, 
and  also  a  complete  workshop  for  carrying  out  repairs. 


68     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

RISING  MAIN. 

The  rising  main  may  of  course  be  of  any  length.  Let 
us  assume  an  average  of  ten  miles.  It  should  be  of  such 
a  diameter  that  the  liquid  maintains  a  velocity  of  3  feet 
per  second  under  normal  working  conditions.  At 
times  of  maximum  flow,  when  reserve  pumps  are  kept 
running  to  deal  with  flood  water,  there  will  of  course 
be  excessive  frictional  head,  but  this  cannot  be  avoided, 
as  it  would  not  be  economically  sound  either  in  capital 
cost  or  maintenance  to  lay  a  larger  pipe  than  suitable 
for  normal  conditions.  Neither  is  there  any  economy 
in  laying  two  mains.  Friction  would  be  increased,  and 
reduction  in  capacity  from  internal  fouling  would  be 
greater.  Again,  double  the  number  of  valves  and  fittings 
would  be  required. 

Cast-iron  spigot  and  socket  pipes  are  to  be  preferred, 
though  steel,  specially  coated,  and  reinforced  concrete 
have  claims  to  be  considered  under  favourable  circum- 
stances. The  main  will  be  divided  into  sections,  accord- 
ing to  grades,  and  each  section  will  require  sluice  valves, 
scour  pipes,  air  valves,  etc.,  arranged  in  suitable  positions. 

WORKING  OF  PUMP  STATION. 

The  power  is  the  steam  generated  in  the  boilers  and 
conveyed  to  the  steam  cylinders  for  actuating  the  engine. 
The  main  sewer  will  discharge  into  the  screening  chamber. 
Heavy  matter,  stones,  and  sand  will  sink  to  the  bottom 
to  be  raised  by  the  dredging  buckets.  Sticks  and  float- 
ing material  will  lodge  against  the  bars  of  the  screens 
and  be  removed  by  the  chain  rakes,  and  the  liquid  will 
pass  to  the  sump  from  which  the  suction  pipes  draw 
their  supply.  Each  pump  will  have  a  separate  suction, 
but  may  discharge  a  common  main.  The  efficiency  of 


COMMERCIAL  EFFICIENCY  69 

this  operation  of  passing  the  sewage  from  the  sump  to 
the  rising  main  will  depend  entirely  on  the  pump  valves, 
provided  the  suction  is  free  from  leakage,  and  the  pump 
is  so  designed  that  it  is  free  from  air  pockets. 

PUMPING  INSTALLATIONS  :  ADVANTAGES  AND  MERITS. 

The  outstanding  advantage  of  a  single  pump-station 
is  that  the  work  to  be  done  is  concentrated,  therefore 
the  maximum  use  can  be  made  of  the  motive  power. 
An  installation  of  this  description  is  the  most  mechani- 
cally efficient  method  of  raising  sewage  known,  as  has 
already  been  shown.  And  the  reason  is  : 

1.  That  the  motive  power  and  the  work  to  be  done 
act  on  one  another  without  the  interposition  of  a  secondary 
power  or  mechanical  motion  beyond  the  reciprocating 
action  of  the  steam  piston  and  the  pump  ram  connected 
by  the  piston  rod. 

2.  That  it  is  possible  to  convert  the  maximum  per- 
centage of  the  motive  fluid  into  useful  work  with  a 
minimum  of  loss  from  dissipation  and  friction. 

The  initial  pressure  of  the  steam  is  absorbed  and  given 
out  in  a  perfectly  uniform  manner  by  means  of  a  suitable 
flywheel  or  compensating  cylinders,  which  are  balanced 
by  differential  accumulators  and  the  pressure  in  the 
rising  main.  Though  so  mechanically  efficient  we  cannot 
avoid  bringing  the  working  parts  of  the  pump,  like  valves 
and  pump  rams,  in  contact  with  the  erosive  fluid,  and 
though  they  can  be  kept  efficient  it  is  only  at  some 
labour  and  expense.  The  screening  chamber,  and  con- 
stant work  connected  therewith,  is  all  labour  and  repair 
due  to  the  pump.  Commercially  what  we  gain  in  the 
power  end  we  are  liable  to  lose  in  the  water  end,  without 
able  supervision.  The  greater  the  pressure  the  more 
efficient  is  this  method  compared  to  any  other,  but  there 


70     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

is  a  limit  in  the  downward  scale,  when  it  is  less  costly 
to  adopt  other  means  though  mechanically  less  efficient. 
The  nature  of  the  fluid  and  the  head  of  water  it  is  desired 
to  pump  against  are  the  deciding  factors. 

EJECTOR  INSTALLATION  :  SUMMARY. 

At  first  sight,  compared  to  a  compact  pumping  plant, 
an  ejector  system  is  a  complicated  network  of  inefficient 
units,  that  would  appear  to  require  an  immense  staff 
and  endless  repairs.  An  installation  that  will  raise  eight 
or  nine  million  gallons  a  day  to  a  height  of  50  feet,  may 
be  divided  up  as  follows  for  the  purpose  of  comparison  : 

1.  Engine  and  boiler  house,  chimney  shaft. 

2.  Engines  and  air  compressors. 

3.  A  number  of  ejector  stations. 

4.  Distributing  air  mains. 

5.  A  number  of  sealed  sewage  mains. 

Assuming  the  engines  for  compressing  the  air  are 
of  the  triple  expansion  horizontal  type,  though  the 
vertical  type  will  take  up  less  room,  a  building  of  less 
height  and  massiveness  will  be  required  than  for  the 
pumps,  and  a  basement  only  will  be  necessary. 

A  good  example  of  an  installation  of  this  type  is 
shown  in  Plate  XIV.  and  Plate  XV.  Though  they  are 
extravagant  in  floor  space  they  are  economical  in  head 
room.  Compared  to  a  vertical  steam  pump  we  have 
only  two  '  floors  '  in  place  of  five,  and  there  is  less 
labour  in  attending  to  the  engines. 

The  boilers  will  probably  be  of  the  water-tube  type, 
and  the  usual  auxiliaries,  consisting  of  electric  light 
engines,  economisers,  cooling  pond  for  the  circulating 
water,  will  complete  the  station.  An  ample  water 
supply  must  be  provided  either  from  the  town  water 
supply  or  other  source. 


COMMERCIAL  EFFICIENCY  71 

EJECTOR  STATIONS. 

The  number  of  the  ejectors  and  the  chambers  in  which 
they  are  placed  will  depend  on  th^  magnitude  and  levels 
of  the  area  to  be  sewered.  Assuming  these  chambers 
are  cast-iron  tubbings,  they  will  range  from  8  feet  to  20 
feet  in  diameter,  and,  with  few  exceptions,  are  sunk 
directly  beneath  the  streets.  Each  tubbing  will  contain 
two  or  more  ejectors,  the  details  of  which  have  been 
explained  at  length  in  Chapter  II. 

Am  MAINS. 

Sixty  ejector  stations  will  require  about  twenty-eight 
miles  of  cast-iron  spigot  and  socket  air  main,  ranging 
from  2J  to  21  inches  in  diameter,  laid  2  or  3  feet  below 
the  surface  of  the  street.  Air  valves,  drain  cocks, 
surface  boxes  must  also  be  provided. 

SEALED  SEWAGE  MAINS. 

These  rising  mains  from  the  ejector  stations  will 
amount  to  another  twenty-five  miles  of  cast-iron  spigot 
and  socket  pipe,  with  the  usual  accessories.  In  many 
cases  they  can  be  laid  in  the  same  trench  as  the  air  mains, 
thus  avoiding  some  expense  in  construction. 

WORKING  OF  EJECTOR  SYSTEM  :  COMPRESSING  AIR. 

The  power  is  the  steam  generated  in  the  boilers  and 
conveyed  to  the  steam  cylinders  for  actuating  the  engines. 
The  air  to  be  compressed  is  cooled  by  an  open  air  evaporat- 
ing device,  consisting  of  a  circular  masonry  chamber, 
in  which  roofing  tiles  are  arranged  on  a  suitable  frame 
beneath  a  water  sprinkler.  Beneath  this  roof  the  air 
intake  is  situated.  From  this  device  the  air  passes  by 
means  of  a  36-in.  pipe  to  ducts  beneath  the  compress- 
ing cylinders,  which  are  jacketed  and  cooled  by  a  pump 


72     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

attached  to  the  crank  shaft  of  each  engine.  From  the 
compressor  the  air  passes  through  a  multi-tubular  after- 
cooler,  and  thence  into  the  collecting  main,  which  dis- 
charges into  two  steel  receivers  of  sufficient  capacity  to 
maintain  a  uniform  flow.  From  these  receivers  the  air 
may  flow  through  a  meter  to  the  distributing  main  for 
working  the  ejectors. 

Alongside  each  ejector  is  situated  a  street  manhole, 
from  which  the  sewage  gravitates  into  the  body  of  the 
ejector,  and  is  automatically  forced  into  the  rising  main 
every  few  minutes. 

EJECTOR  INSTALLATIONS  :  ADVANTAGES  AND  MERITS. 

The  outstanding  advantage  of  the  ejector  system  is 
that  we  have  no  sump  or  screening  chamber.  But  we 
have  to  employ  a  secondary  power — that  is,  the  motive 
power,  instead  of  being  applied  directly  to  the  work 
to  be  done,  has  to  be  converted  to  another  power  before 
it  can  be  so  applied.  In  this  process  we  sacrifice  effi- 
ciency. Again,  owing  to  the  nature  of  the  secondary 
power — that  is,  the  compressed  air — the  process  of  con- 
version at  the  higher  pressure,  which  would  be  required  to 
do  the  work  that  is  done  by  the  reciprocating  pump,  is 
wasteful  and  costly.  The  ejector,  it  must  be  borne  in 
mind,  corresponds  to  the  water  end  of  the  pumping 
engine,  but  it  may  be  located  miles  away  from  the  steam 
end.  The  compressed  air  is  simply  the  medium  of 
transmission. 

In  the  ejector,  however,  the  secondary  power  is  applied 
directly  to  the  work  to  be  done  without  the  interposition 
of  mechanical  motion.  Therefore  there  are  no  working 
parts,  practically  speaking,  in  contact  with  an  erosive 
fluid.  Again,  there  is  no  constant  pulsation  of  the 
valve :  it  opens  once  for  a  single  discharge.  The  lower 


COMMERCIAL  EFFICIENCY  73 

the  air  pressure  required  the  higher  the  efficiency,  as  a 
smaller  volume  of  air  is  required  to  raise  a  given  volume 
of  sewage. 

CAPITAL  COST. 

Exclusive  of  land,  the  capital  cost  includes  every  ex- 
pense that  occurs  under  the  five  items  mentioned  above. 

The  advocates  for  installing  pumps  in  place  of  ejectors, 
when  both  have  equal  claims,  invariably  put  forward 
the  plea  of  reduced  capital  outlay.  Heretofore  this 
claim  was  without  doubt  justified,  but  was  almost  entirely 
due  to  the  absence  of  competition  in  manufacture,  and 
the  expense  of  economical  compressing  engines.  At 
the  present  day  this  is  by  no  means  the  case. 

In  this  case  both  the  installations  briefly  outlined  are 
of  great  magnitude, and  the  cost  of  each  exceeded  £300,000, 
but  there  was  a  difference  of  only  15  per  cent,  in  favour 
of  the  pumps.  When  a  multiple  ejector  system  dis- 
charges direct  to  the  disposal  works  in  place  of  a  single- 
pump  station,  the  greatly  reduced  cost  of  constructing 
shallow  sewers  must  not  be  lost  sight  of. 

In  raising  crude  sewage  it  is  not  only  the  value  of  the 
work  done  that  should  be  considered,  but  the  way  that 
work  is  done  and  the  means  employed  to  do  it. 

For  instance,  we  might  install  a  highly  efficient  plant, 
commercially,  at  a  small  capital  cost ;  but  it  might 
perform  its  work  in  such  a  manner  as  to  render  the 
locality  uninhabitable.  The  cost  per  given  volume 
raised  is  of  strictly  relative  value  to  other  conditions 
being  fulfilled  and  by  no  means  the  only  factor  to  be 
decided,  any  more  than  the  contractors'  mechanical 
efficiency  trial  can  be  taken  as  a  proof  of  economical 
working  over  a  number  of  years  under  daily  working 
conditions. 


74     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

MAINTENANCE. 

It  is  often  assumed  that  the  most  efficient  device 
mechanically  will  be  the  most  economical  in  upkeep 
and  maintenance.  It  should  be  so,  as  the  cost  of  fuel 
consumed  to  generate  the  motive  power  is  usually  the 
largest  item  in  the  balance  sheet  ;  but  it  is  by  no  means 
always  the  case.  Pumps  and  ejectors  for  raising  sewage 
are  invariably  in  the  hands  of  municipalities  and  corpora- 
tions, and  the  cost  of  maintenance  is  usually  accepted 
as  an  inevitable  item  of  expense  whatever  it  may  be, 
regardless  of  the  fact  that  in  many  cases  by  insisting 
on  essentials  being  kept  in  the  highest  state  of  repair 
and  suppressing  the  superfluous,  economies  of  even  50 
per  cent,  may  be  effected.  But  it  requires  an  experi- 
enced engineer  to  do  this  with  a  free  hand  and  a  con- 
scientious interest  in  the  machinery  under  his  care. 

It  is  difficult  to  magnify  the  immense  discrepancies 
that  may  exist  between  two  power  systems  in  the  matter 
of  running  costs,  or  the  extent  to  which  secondary  matters 
will  be  permitted  to  nullify  the  benefits  of  heavy  capital 
expenditure. 

REPOBTS. 

Whatever  the  installation  may  be,  the  commercial 
efficiency  will  largely  depend  on  careful  supervision  and 
accurate  records  from  which  reports  can  be  compiled, 
in  order  that  one  year  may  be  compared  with  another 
and  estimates  made  in  advance  of  what  will  be  required. 
It  is  often  as  wasteful  to  order  too  much  in  advance  as 
it  is  false  economy  to  cut  down  requirements  that  increase 
efficiency. 

Reports  should  be  brief  and  concise,  and  records  of 
expenditure  tabulated  in  their  simplest  form.  They 
should  commence  with  a  paragraph  stating  the  object 


COMMERCIAL  EFFICIENCY  75 

of  the  installation,  at  the  same  time  giving  a  summary 
of  the  plant,  together  with  its  power  and  capacity,  as 
with  changes  in  administration  it  may  be  quite  unknown 
to  those  to  whom  the  report  is  submitted.  The  exist- 
ing condition  of  the  machinery,  replacements  required, 
quantity  of  stores  consumed,  and  on  hand,  number  of 
staff  and  their  wages,  with  all  suchlike  information, 
should  be  given  in  detail. 

If  monthly  reports  have  previously  been  made,  no 
difficulty  will  be  experienced  in  collecting  such  informa- 
tion, which  in  turn  is  compiled  from  a  day  book  kept 
in  the  power  house  and  filled  in  by  the  driver.  This 
book  should  be  divided  into  columns  and  record  the 
number  of  the  units  in  use,  revolutions  per  minute  made 
by  the  engine  each  shift,  the  weight  of  fuel  consumed, 
steam  pressure  maintained,  gauge  pressure,  and  any 
unusual  incidents. 

DAILY  DISCHARGE. 

In  a  pumping  installation  the  volume  raised  may  be 
calculated  from  the  revolutions  of  the  engine,  but  pro- 
vision should  be  made  for  checking  the  discharge  periodi- 
cally. Any  serious  falling  off  will  be  observed  from  the 
records,  as  the  pump  would  either  have  to  increase  its 
speed  or  additional  power  would  have  to  be  employed 
to  keep  the  sewage  at  the  required  level. 

In  the  case  of  ejectors  each  one  is  provided  with  an 
automatic  counter,  and  the  strokes  are  recorded  every 
two  or  three  days,  from  which  it  is  easy  to  calculate  the 
discharge. 

Taking  one  day  with  another,  there  is  little  variation 
in  the  discharge  from  sewers  in  the  absence  of  rain  ;  but 
the  variation  in  the  twenty -four  hours  is  of  great  magni- 
tude according  to  the  time  of  day. 


76     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

It  is  now  proposed  to  give  examples  of  the  actual 
yearly  maintenance  costs  of  three  methods  of  raising 
sewage — that  is,  by  the  reciprocating  pump,  the  centri- 
fugal pump,  and  the  pneumatic  ejector,  all  pumping 
from  the  same  source.  In  every  case  these  costs  are 
much  higher  than  exist  in  England  ;  but  that  is  of  little 
consequence,  as  they  are  given  for  the  sake  of  compar- 
ing one  system  with  another  under  similar  conditions 
of  labour  and  maintenance. 

In  the  first  two  tables  the  pumps  are  driven  by  electric 
motors,  to  which  current  was  supplied  at  the  rate  of 
2d.  to  4d.  a  unit,  an  almost  prohibitive  figure.  On  the 
other  hand,  in  the  third  table  coal  was  supplied  to  the 
power  house  at  £3,  6s.  2d.  per  ton,  which  is  no  less 
expensive  in  comparison. 


COMMERCIAL  EFFICIENCY 


77 


MAINTENANCE  TABLES  :  PUMPS. 


'  A.'  Maintenance  of  12  in.  X 12  in.  Reciprocating  Pump 


STAFF 


No. 

Occupation. 

Rate  per           Rate  per 
month.                year. 

Totals. 

— 

1 

£   s.    d.  i       £   s.    d. 

1 

Electrician     . 

12     6     8     148    0    0 

1 

Mechanic 

946     110  14    0 

2 

Greasers 

316       73  16    0 

1 

Labourer 

226       25  10    0 

1 

Watchman     . 

200       24    0    0 

£382    0    0 

POWER,  STORES,  REPAIRS,  ETC. 

£       s.   d. 

Electric  current  power  account 

1263    6    8 

1263    6    8 

Lubricating  oil 

732 

Waste,  soap,   polish, 

emery, 

cleaners,  etc.    . 

15    0    0 

Hydraulic  packing  for  pump 

ram          .... 

11     8    5 

Valve  leather       , 

7    0     1 

Gauge  glasses,  paint, 

etc.      . 

390 

Incandescent  lamps 

0  15    0 

Disinfectant         *  « 

263 

Three  cast-iron  rams, 

less  old 

rams  as  scrap  brass  . 

472 

51     9     1 

Current  for  lighting  station  . 

18    2    6  ! 

Fresh  water 

21     3     7         39    6     1 

| 

j£1736     1  10 

i 

The  volume  of  crude  sewage  discharged  for  this  expenditure 
at  280  head=90,684,880  gallons. 

Therefore  the  cost  per  1000  gallons=4'59  pence. 


78     EFFICIENCY  OF  PUMPS  AND  EJECTORS 


'B.'  Maintenance  of  14-m.  Centrifugal  Pump 
STAFF 


No.           Occupation. 

Rate  pel- 
month. 

Rate  per 
year. 

Totals. 

£    A\    d. 

£   s.    d. 

1        Electrician     . 

12    6    8 

148    0    0 

1        Mechanic      •«• 

946 

110  14    0 

2       Greasers         . 

3     1     6 

73  16    0 

1       Labourer 

226 

25  10    0 

1       Watchman     ;; 

200 

24    0    0     £382    0    0 

POWER,  STORES,  REPAIRS, 

ETC. 

£    s.    d. 

Electric  current  power  account 

264    5     7 

264    5    7 

r  ' 

Lubricating  oil      * 

f.'  * 

2  18    0 

Cotton  waste 

''•'•»         •  • 

358 

Paraffin         .  * 

4 

1  11     6 

Grease 

. 

094 

1  Soap,  polish,  and  emery 

2  13    6 

1  Floor  cloth   . 

.         . 

0  15    0 

i  Brushes         « 

*• 

1  14    S 

Hose  and  couplings 

. 

1     3    3 

Insertion  for  joints 

. 

2  17     5 

Flexible  cable       .% 

075 

1J  W.I.  piping      t* 

. 

1  14    3 

Copper  sheet         * 

. 

0  12    0 

Switch  repairs     .  . 

0  13    3 

Sundries        .      --£' 

•:'•. 

0  14    7         21     9  10 

Fresh-water  supply 

. 

73     6    0 

Current  for  lighting 

f  :• 

12    0    0         85    6    0 

1 

£753     1     5 

The  volume  of  crude  sewage  discharged  for  this  expenditure 
at  8  ft.  head= 133,640,749  gallons. 

Therefore  the  cost  per  1000  gallons- 1-35  pence. 


COMMERCIAL  EFFICIENCY  79 


MAINTENANCE   COSTS  OF  RECIPROCATING  AND   CENTRI- 
FUGAL PUMPS. 

Table  '  A '  shows  the  yearly  expenses  in  running  a 
three-throw  12  in.  X 12  in.  single-acting  ram  pump,  driven 
by  a  64  horse -power  motor.  Considering  the  great 
head  and  nature  of  the  effluent  which  was  heavily 
charged  with  cab-rank  refuse  and  road  grit,  together 
with  the  high  cost  of  the  power,  the  rate  is  not  ex- 
cessive. 

Table  '  B  '  shows  the  yearly  expense  of  running  a 
14-in.  centrifugal  pump  drawing  from  the  same  sump. 
This  pump  was  fixed  below  the  level  of  the  water  in  the 
sump,  and  was  driven  by  a  vertical  shaft  coupled  to  a 
25  horse -power  motor. 

The  wages  of  the  staff  are  the  same,  but  with  only 
8  ft.  head  the  power  consumed  was  much  less.  On  the 
other  hand,  a  constant  supply  of  fresh  water  under 
pressure  was  required  for  the  forced  lubrication  of  the 
thrust  bearing  and  impeller.  Even  then  the  impeller 
had  to  be  withdrawn  every  few  weeks,  to  clear 
fibrous  matter  and  obstructions  from  the  impeller 
ducts. 

In  neither  of  these  tables  has  the  interest  on  capital 
cost  been  allowed  for  ;  but  the  Electric  Light  Company's 
profit  is  included  in  the  cost  of  the  power. 

The  capital  cost  of  the  ram  pump  is  of  course  higher, 
as  would  be  expected  with  the  greater  power.  On  the 
other  hand,  no  deep  underground  chamber  is  required 
in  which  to  erect  the  pump,  and  there  would  be  little 
difference  in  the  total  cost  including  buildings.  Both 
plants  were  run  with  twelve -hour  shifts,  but  eight  hours 
is  to  be  recommended. 


80     EFFICIENCY  OF  PUMPS  AND  EJECTORS 


MAINTENANCE  TABLES  :  EJECTORS. 

1 C.'  Maintenance,  Ejector  System 


STAFF 


No. 

1 

Occupation. 

Rate  per 
i       month. 

• 

Rate  per 
year. 

Totals. 

£   s.    d. 

£      S.    d. 

£      8.    d. 

3 

Drivers  .         „ 

836 

294    6    0 

3 

Firemen 

347 

116    5    0 

6 

Greasers 

315 

221     3    0 

2 

Greasers 

237 

52    6    0 

2 

Fitters   .         , 

3  15    0 

90    0    0 

6 

Labourers 

1  17    5 

134     8    0 

2 

Trimmers 

1  17     5 

44  18    0 

953     6    0 

1 

Electrician 

14     5     6 

171     7     0 

1 

Wireman 

2  10    0 

27    0    0 

4 

Watchmen     -,.<  , 

227 

102     4    0 

300  11     0 

1 

Mechanic 

946 

110  14    0 

2 

Inspectors 

3     1     5 

73  14    0 

2 

Labourers 

1  17     5 

42  18    0 

2 

Boys 

1  11     2 

38    8    0 

265  14    0 

Casual  labour 

141     0    0 

141     0    0 

£1660  11     0 

COMMERCIAL  EFFICIENCY 


81 


'  D.'  Maintenance,  Ejector  System 


STORES,  REPAIRS,  ETC. 

Coal,  200  tons  at  £2,  4s.  2d.         £ 

8. 

d. 

£   s.    d. 

per  ton    . 

441 

13 

4 

Coal,  1069  tons  at  £3,  6s.  2d. 

per  ton    ,      .'•;/       1         .       3536 

12 

2 

3978     5     6 

Cylinder  oil       ./«•         .        ^:          92 

1 

3 

Journal  oil           .          .         .  .         75 

2 

o  I 

Crank  chamber  oil        .         »  $        29 

12 

5 

Diesel  oil    .      '   „         '*"'       *:            9 

3 

7 

Cotton  waste       .         ?>        ...          79 

9 

6 

Rags  (cleaning)    .         .         ,             4 

19 

5 

Grease  and  tallow         ,      *  . 

7 

9 

7 

Soft  soap,  soda,  polish,  etc.  . 

51 

18 

5 

349  16    2 

Brooms,  brushes,  cloths        * 

13 

2 

0 

Oil  trays,  valve  springs         * 

15 

17 

6 

Electric  lamps,  wire,  etc. 

13 

19 

1 

Gauge  glasses  and  fittings 

11 

16 

1 

Twist  drills,  saw  blades 

13 

11 

6 

Fire  bricks  and  fire  clay        . 

7 

8 

9 

Files,  washers,  tool  steel       .  ! 

10 

11 

2 

Asbestos  and  hemp  packing             41 

0 

3 

Drugs  and  distemper    .          .              6 

7 

0 

W.I.  piping,  unions,  and  fittings         22 

18 

3 

Pig  lead,  firewood,  and  yam             24 

15 

0       181     7    4 

Repairs  to  machinery  .         *.          59 

17 

6  | 

Roads  and  buildings  repairs           193 

15 

0 

Paint,  composition,  etc. 

118 

15 

o 

Sundries      .         ;      *  .  "'.<      .           95 

17 

8 

Ejector  spares     „         .         .            35 

4 

6       503    9    8 

Venturi  meter  flushing  water           49 

6 

10  1 

Power-house  water  supply    . 

489 

11 

7 

Garden  water,  unfiltered 

26 

11 

2       565    9     7 

£5578    8    3 

Wages  of  staff          v 

1660 

11 

0  I  1660  11     0 

|£7238  19    3 

The  volume  of  crude  sewage  discharged  for  this  expenditure 
at  50  ft.  head=884,126,980  gallons. 

Therefore  the  cost  per  1000  gallons=l-96  pence. 

F 


82     EFFICIENCY  OF  PUMPS  AND  EJECTORS 


MAINTENANCE  COSTS  OF  EJECTOR  SYSTEM. 

Tables  '  C  '  and  '  D  '  show  the  maintenance  costs  for 
one  year  of  an  ejector  system.  Of  63  ejector  stations, 
36  were  in  daily  use.  These  figures  include  52  miles  of 
pressure  mains  besides  the  power  house. 

It  will  be  observed  from  the  list  '  C  '  giving  the  staff 
that  most  of  the  labour  is  absorbed  by  the  power  house. 
Examination  of  the  various  items  on  list  '  D  '  shows 
there  has  been  no  attempt  at  economy  and,  with  the 
exception  of  labour  which  is  cheap,  that  rates  are  much 
in  advance  of  those  in  England.  Some  items,  such  as 
repairs  to  roads  and  buildings,  include  details  that 
should  be  credited  to  other  sections,  and  the  large  figures 
for  water  supply  were  of  a  purely  temporary  character, 
owing  to  its  being  necessary  to  draw  water  for  con- 
densing purposes  from  the  city  mains  pending  the 
construction  of  the  necessary  works  for  the  station's 
permanent  supply.  The  object  of  giving  these  details  is 
not,  as  before  stated,  in  order  to  claim  or  demonstrate 
how  economically  or  extravagantly  crude  sewage  can 
be  raised,  but  solely  for  the  purpose  of  comparing  one 
system  with  another  under  the  same  conditions  of  super- 
vision and  pumping  the  same  effluent.  Herein  lies  the 
value  of  the  figures  given. 

To  compare  a  ram  pump  in  England  with  a  centri- 
fugal pump  in  India  and  an  ejector  system  in  Spain, 
is  of  little  value  if  we  wish  to  arrive  at  figures  for  the 
purpose  of  comparison.  For  the  same  reason  interest 
on  capital  is  not  given,  as  land  and  buildings  should 
be  included,  and  there  is  no  object  in  comparing  such 
values. 


COMMERCIAL  EFFICIENCY  83 

MAINTENANCE  :  DIFFICULTIES  OF  COMPARISON. 

Explicit  information  from  a  variety  of  sources  is  diffi- 
cult to  obtain,  and  it  is  still  more  difficult  to  draw  up 
a  table  of  fair  comparisons  between  running  plants. 
Local  circumstances  and  conditions  prohibit  the  various 
items  of  expenditure  from  being  tabulated  on  the  same 
basis.  In  one  locality  fuel  will  be  expensive  and  labour 
cheap.  Cheap  labour  is  invariably  inefficient,  and  what 
is  saved  in  this  respect  is  taken  out  in  repairs. 

Again,  corporations  and  municipalities  often  derive 
their  power  for  lifting  sewage  from  rubbish  destructors, 
and  in  such  cases  the  costs  of  the  power  would  be  lower, 
whether  pumps  or  ejectors  were  utilised.  On  the  other 
hand,  unless  very  precise  details  and  records  were  kept 
it  would  be  difficult  to  decide  to  what  extent  the  trans- 
port and  handling  of  such  rubbish  should  be  debited  to 
the  cost  of  raising  the  sewage. 

Other  matters  of  controversy  could  be  suggested,  and 
those  who  are  familiar  with  the  subject  will  appreciate 
the  fact  that  unless  the  conditions  of  supervision,  labour, 
stores,  fuel  are  the  same,  besides  raising  the  same  effluent 
as  in  these  examples,  misleading  conclusions  may  be 
arrived  at. 

Much  depends  on  the  knowledge  and  interests  of  the 
responsible  authorities  and  supervising  staff.  The  idea 
that  an  economical  plant  will  remain  economical  without 
unremitting  attention,  no  matter  of  what  type  it  may  be, 
is  a  fallacy  ;  but  it  can  be  stated  with  confidence  that 
the  simplest  machinery  is  the  cheapest  to  run.  The 
locality  which  enables  the  whole  of  the  effluent  to  be 
raised  by  a  single-power  engine,  whether  pump  or  ejector, 
will  have  a  great  advantage  in  costs  over  a  sectional 
system. 


84     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

In  comparing  expenses  the  magnitude  of  the  power, 
total  volume  and  head  of  water  must  be  borne  in  mind, 
as  the  greater  the  volume  the  cheaper  it  is  to  lift  per 
1000  gallons. 

Maintenance  consists  of  supervision,  fuel,  repairs,  and 
consumable  stores. 


1  E.'  Commercial  Efficiency  :  Table  of  Pumps  and 
Ejectors 

COST   OF   RAISING   CRUDE   SEWAGE 


Cost  it 

i  pence.     , 

Ref. 

Type  of  Engine. 

Head. 

Per 
1000 

Per  100  j  volume,  gaiions. 
ft.  head 

gallons. 

per  1000 
gallons. 

A 

Reciprocating 

pump 

290  ft. 

4-475 

1-543         86,169,373 

B 

Centrifugal 

pump 

8  „ 

1-421 

17-762       141,757,973  j 

C 

Ejectors  (72) 

50  „ 

1-466 

2-940       884,596,791 

» 

Reciprocating 

117   „ 

1-364 

1-166    1,111,250,314 

pump 

E 

Ejectors  (39) 

44  „ 

0-625 

1-420  ; 

F 

Ejectors 

65  „ 

1-410 

2-169       790,000,000 

G 

Ejectors 

40   „ 

2-000 

5-000       273,750,000 

! 

In  the  last  column  but  one  the  cost  per  1000  gallons 
per  100  ft.  head  is  given  in  the  above  table,  as  the  author 
is  well  aware  that  it  is  usually  considered  a  recognised 
standard  of  comparison  ;  but  it  is  submitted  that  in 
practice  it  is  of  purely  academic  value,  as  it  is  obvious 
if  we  only  require  to  raise  the  effluent  50  feet,  it  is  quite 
immaterial  if  the  apparatus  installed  is  inefficient  and 
costly  when  called  upon  to  raise  sewage  100  feet. 


COMMERCIAL  EFFICIENCY  86 

It  is  clear  that  the  commercial  efficiency  of  the  ejector 
is  not  far  short  of  the  reciprocating  pump,  and  the  centri- 
fugal pump  falls  short  of  both.  When  it  is  remembered 
that  the  steam  consumed  per  indicated  horse -power  per 
hour  for  '  D  '  is  only  9*75  Ibs.  in  place  of  15'32  Ibs.  per 
hour  for  '  C,'  it  is  obvious  that  if  the  ejector  system  was 
actuated  by  such  an  economical  steam  engine,  there 
would  be  little  to  chose  between  the  two  systems. 

'A,'  'B,'  4C,5  'D'  are  all  raising  the  same  effluent 
heavily  charged  with  grit  and  refuse.  *  A/  'B'  are 
driven  by  electric  motors  for  which  the  current  is  pur- 
chased and  therefore  includes  a  commercial  profit. 

In  comparison  with  '  D,'  '  A  '  has  the  advantage  of  a 
high  piston  speed  and  multiple  clear-way  valves,  whereas 
'  D  '  has  a  low  piston  speed  and  large  rectangular  valves. 
The  trial  results  of  '  D  '  are  shown  on  page  66,  and  '  A ' 
is  the  12  in.  X 12  in.  pump  on  the  diagram,  Plate  XI. 

The  poor  result  and  high  cost  (if  the  8-ft.  head  is  taken 
into  consideration)  of  the  centrifugal  pump  is  due  to  slip 
and  loss  of  velocity,  and  though  the  cost  of  pumping 
with  the  6-in.  centrifugal  pump  on  Plate  XI.  could  not 
be  ascertained,  it  would  hardly  have  made  a  better 
showing. 

The  first  four  pumps  in  Table  '  E '  are  employed  on  the 
Cairo  main  drainage.  E  is  the  ejector  system  at  Gosport, 
England,  and  without  doubt  gives  a  most  economical 
result.  F  is  the  Karachi  system,  India,  and  G  the  South- 
ampton system,  England.  The  author  is  indebted  to  the 
Chief  Engineers  of  Gosport,  Karachi,  and  Southampton 
for  the  figures  for  these  places. 

Individual  instances  could  no  doubt  be  given  that 
would  apparently  refute  these  figures  and  show  that 
both  the  reciprocating  pump  and  the  centrifugal  pump 
will  raise  sewage  at  a  much  lower  rate  per  1000  gallons, 


86    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

but  it  would  probably  be  found  that  more  favourable 
circumstances  existed. 

For  instance,  an  installation  of  centrifugal  pumps 
driven  by  internal-combustion  engines,  dealing  with 
diluted  sewage  and  storm  water  in  large  quantities, 
would  show  a  greatly  reduced  figure,  even  allowing  for 
replacing  the  whole  of  the  pumps  after  a  few  years  ;  but 
it  must  be  distinctly  understood  that  this  table  does 
not  refer  to  such  conditions,  but  the  raising  of  crude 
sewage  as  herein  defined,  that  is,  an  effluent  discharged 
by  city  sewers,  containing  every  conceivable  substance 
that  may  cause  obstruction  or  destruction  to  mechanical 
parts. 


CHAPTER  V 

STAFF:  SUPERVISING 

IN  large  cities  the  drainage  staff  will  only  be  a  section 
of  the  public  service.  In  urban  districts  the  Borough 
Engineers  will  probably  have  full  direction  of  such  works. 

Let  us  assume  the  installations  to  be  constructed  and 
supervised  are  of  such  magnitude  as  those  described  in 
the  last  chapter. 

There  will  be  a  chief  engineer  and  his  assistants  for 
drawing  up  designs,  specifications  and  estimates,  and 
examining  tenders ;  a  resident  engineer  and  his  staff 
of  inspectors  for  supervising  the  construction  and  making 
out  contractors'  monthly  certificates  for  payment ;  and 
eventually  a  running  staff,  which  will  be  organised  as 
the  works  are  completed.  In  drainage  schemes  the 
constructional  work  may  still  be  in  progress  after  the 
running  staff  have  commenced  their  duties,  especially 
in  an  ejector  system,  as  one  of  its  principal  merits  con- 
sists of  being  able  to  lay  down  new  ejector  areas  as 
required,  instead  of  having  to  complete  the  whole  system 
in  a  single  contract.  By  this  means  the  machinery  is 
brought  into  use  as  soon  as  it  is  put  down  and  does  not 
have  to  remain  rusting  in  the  ground  as  buried  capital. 

Every  man  on  the  staff  cannot  be  an  experienced 
engineer,  but  for  economical  construction  it  is  absolutely 
necessary  that  at  least  half  the  number  employed  should 
have  had  a  sound  practical  training  in  the  particular 

87 


88     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

class  of  work  they  are  called  upon  to  supervise :  especially 
those  who  have  to  decide  technical  questions  and  deal 
with  contractors. 

Paper  qualifications  are  excellent  things,  but  too  much 
reliance  should  not  be  placed  upon  them,  and  it  is  the 
height  of  foolishness  to  rule  out  an  otherwise  able  man 
because  he  does  not  possess  certain  degrees  or  academic 
distinction.  It  need  scarcely  be  remarked  that  appoint- 
ments by  influence  on  a  technical  staff  can  only  result  in 
waste,  extravagance,  and  friction.  In  selecting  officers 
for  technical  posts  we  want  to  know  exactly  what  their 
experience  has  been.  If  they  possess  academic  degrees, 
so  much  the  better,  but  we  must  know  how  they  were 
obtained  and  what  they  were  for. 

For  instance,  an  academic  honour  bestowed  on  a 
student  for  a  treatise  on  the  theory  of  the  gas  engine 
is  of  no  economic  advantage  in  drawing  up  a  specifi- 
cation for  a  pneumatic  ejector  system.  In  the  same 
way,  the  construction  of  weirs  and  sea  walls  is  not  an 
efficient  training  ground  for  the  supervision  of  a  tram- 
way power  station. 

Of  all  the  various  branches  of  engineering  there  is  less 
information  concerning  drainage  work  to  be  derived 
from  text -books  and  theory  than  in  any  other.  Such 
work  cannot  be  standardised  except  in  mechanical 
detail.  Each  scheme  has  to  be  considered  on  its  merits, 
and  the  wider  the  experience  of  the  responsible  engineer, 
the  better  he  is  able  to  adapt  available  means  to  suit 
his  purpose. 

This  is  not  the  place  to  enter  into  the  merits  and  fail- 
ings of  the  training  of  the  average  engineer  in  the  public 
service ;  but  it  may  be  said  that  if  he  is  to  occupy  a  re- 
sponsible post,  with  credit  to  himself,  his  work,  and  his 
employers,  the  average  academic  course,  the  pupilage  in 


STAFF:    SUPERVISING  89 

the  office,  the  superficial  'works  training/  the  appointment 
as  'assistant'  to  the  Borough  Engineer,  the  'automatic 
promotion  '  is  rarely  sufficient . 

One  half  of  his  profession  remains  a  closed  book  to 
him.  Efficiency  to  him  is  an  academic  expression. 
There  is  nothing  so  conducive  to  the  development  of 
character  as  having  to  earn  a  living  on  the  training 
you  have  had.  There  is  nothing  so  chastening  to 
youthful  conceit  as  seeking  employment  on  your  merits, 
or  so  injurious  to  initiation  and  resource  as  being 
provided  with  a  comfortable  post  without  the  smallest 
exertion  or  disappointment.  The  consulting  engineer's 
office  will  not  do.  The  public  service  will  not  do.  They 
require  or  should  require  qualified  men  to  design,  ad- 
ministrate, and  supervise  constructional  or  mainten- 
ance work,  and  to  perform  such  functions  with  credit 
the  engineer  must  know  from  precedent  how  the  work 
should  be  done.  He  must  have  obtained  employment 
which  will  have  given  him  an  insight  into  the  great 
realities  of  time,  labour,  and  expenditure,  that  is  to  say, 
he  must  have  gained  experience  in  the  fierce  competitive 
market  of  industrial  enterprise,  which  is  the  constant 
spur  to  efficiency  and  improvement.  It  is  this,  before 
all  else,  that  will  produce  the  man  who  knows  precisely 
what  to  do  and  how  to  do  it  in  after  years.  To  march 
about  a  job  in  progress  without  knowing  the  why  and 
wherefore  of  what  he  sees  is  a  totally  different  thing  to 
having  been  employed  upon  the  work  himself. 

He  cannot  guess  the  contractor's  point  of  view  if  he 
has  not  worked  for  him.  There  is  the  seller's  point  of 
view  and  the  buyer's  point  of  view  to  every  pound 
sterling  worth  of  work  that  is  carried  out. 

There  are  intricate  questions,  apart  from  the  actual 
work,  that  must  be  considered.  For  instance,  there  is 


90     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

the  time  and  labour  that  it  takes  to  perform  a  certain 
task,  administration,  organisation  and  procedure,  and 
the  inevitable  contingencies  which  cannot  be  specified 
in  a  contract.  If  he  is  ignorant  of  such  matters  when 
he  comes  to  hold  a  responsible  position,  his  brain  is 
bankrupt  of  initiative  and  destitute  of  resource  in  those 
difficulties  which  occur  in  every  large  enterprise.  He 
will  be  an  utter  stranger  to  those  small  considerations 
to  a  staff  which  mean  so  much  and  cost  so  little,  but 
promote  harmony  and  efficiency  and  enable  us  to  dis- 
tinguish between  what  is  a  necessity  and  what  is  super- 
fluous. He  must  know  his  men  and  what  they  can  do. 
If  he  does  not  know  the  road  himself  he  cannot  point 
it  out  to  others.  And,  finally,  it  is  the  only  school  in 
which  he  can  learn  to  direct  with  confidence,  argue  with 
force,  protect  his  own  and  his  employer's  interests  from 
commercial  abuses,  and  avoid  being  reduced  to  impotence 
or  being  constantly  imposed  upon  when  his  turn  comes 
to  hold  high  office  in  the  public  services. 

There  is  no  such  thing  as  a  man  who  is  born  with 
experience. 

However,  as  it  is  the  efficiency  of  the  machinery  and  its 
maintenance  that  is  under  discussion,  we  will  now  com- 
pare the  staff  of  a  pumping  station  with  that  of  an  ejector 
system. 

There  is  a  popular  notion  that  the  ejector  system 
requires  a  much  larger  staff  to  keep  it  in  order,  but  this 
is  not  really  the  case. 

PUMPING -STATION  STAFF. 

The  following  table  gives  some  idea  of  the  essential  men 
required  for  routine  work,  allowing  for  three  eight-hour 
shifts.  In  England  it  is  sometimes  the  practice  to  run 
with  only  two  shifts,  but  this  cannot  be  recommended. 


STAFF:   SUPERVISING 


91 


ESSENTIAL  ROUTINE  MEN  FOR  PUMPING  STATION 


Superintendent 

Assistant 

Mechanic 

Mechanic 

Electrician 

Driver 

Driver 

Driver 

Fireman 

Fireman 

Fireman 

Trimmer 

Trimmer 

Trimmer 

Cleaner 

Cleaner 

Cleaner 

Cleaner 

Cleaner 

Cleaner 

Cleaner 

Cleaner 

Cleaner 

Screening  Chamber 


Cleaner 
Labourer 
Labourer 
Labourer 

Cleaner 
Labourer 
Labourer 
Labourer 

Cleaner 
Labourer 
Labourer 
Labourer 

To  this  list  should  be  added  mechanics'  assistants, 
a  clerk,  storekeeper,  telephone  lad,  and  three  or  four 
men  for  cleaning  the  buildings,  say  forty -four  in  all. 


EJECTOR-SYSTEM  STAFF. 

The  following  table  gives  some  idea  of  the  essential 
men  required  for  routine  work.  The  wages  paid  to  such 
men  will  be  seen  on  pages  84  and  86,  but  in  England  the 
scale  would  be  considerably  higher. 


ESSENTIAL  ROUTINE  MEN  FOB  EJECTOR  SYSTEM 

Superintendent 
Assistant 
Mechanic 
Mechanic 


92     EFFICIENCY  OF  PUMPS  AND  EJECTORS 


Driver 

Driver 

Driver 

Fireman 

Fireman 

Fireman 

Trimmer 

Trimmer 

Trimmer 

Cleaner 

Cleaner 

Cleaner 

Cleaner 

Cleaner 

Cleaner 

Ejectors 

Inspector  Inspector  Inspector  Inspector  Inspector 
Assistant  Assistant  Assistant  Assistant  Assistant 
Labourer  Labourer  Labourer  Labourer  Labourer 

Allowing  the  same  number  of  assistants,  etc.,  this  makes 
a  total  of  forty-three  in  all. 

As  a  rule  it  will  be  found  that  extra  hands  and  casual 
labour  omitted  in  both  these  lists  will,  during  the  year, 
amount  to  more  for  the  pumping  station  than  for  the 
ejector  system.  Large  pumps  require  at  least  an  extra 
cleaner  compared  to  compressors,  and  though  there  is 
no  outside  staff,  the  screening  chamber  absorbs  a  lot 
of  labour  both  in  actual  attendance  and  repairs.  Again, 
in  both  these  cases  the  water-tube  boilers  are  oil-fired : 
with  coal,  more  firemen  and  trimmers  are  required.  The 
expense  of  handling  oil  fuel  from  the  railway  to  the 
furnace  is  very  much  less  than  the  expense  of  handling 
coal,  especially  if  it  has  to  be  carted.  Provided  the  air- 
compressing  machinery  is  of  simple  construction,  two 
power  units  of  150  horse -power  each  can  be  kept  running 
by  the  above  staff. 

There  is  little  work  on  air  -  compressing  machinery 
compared  to  that  on  large  pumps,  and  the  mechanic  will 
find  time  to  replace  the  leathers  on  the  ejector  valves 
and  assist  in  testing  the  air  mains.  On  the  other  hand, 
air-compressing  machinery,  with  complicated  gear,  will 
provide  a  great  deal  of  work  to  keep  it  in  an  efficient 
state. 


STAFF:    SUPERVISING  93 

EJECTOR  INSPECTORS'  DUTIES. 

Each  of  the  inspectors  would  be  responsible  for  twelve 
ejector  stations,  ten  miles  of  pressure  mains,  with  an 
aggregate  of  280  valves,  about  half  of  which  would  be 
on  the  ejectors.  They  record  the  counter  readings, 
inspect  the  flap  valves,  fit  the  cup  leathers,  and  see 
that  all  is  in  order.  It  is  also  their  business  to  know 
the  position  of  every  yard  of  main  and  valve  in  their 
section  and  periodically  test  every  length  for  leakage. 
The  labourers  would  work  together,  excavating  joints 
if  not  required  on  the  ejector,  and  must  be  always  pre- 
pared for  any  break -down  work.  On  large  systems 
embracing  many  square  miles  a  light  motor  lorry  is  of 
the  greatest  value  in  picking  up  both  men  and  material 
for  any  repair  work  in  progress. 

Time  spent  on  the  organisation  and  supervision  of 
the  working  staff  is  never  wasted.  In  a  pumping  in- 
stallation the  men  work  under  the  eye  of  the  engineer 
in  charge.  In  the  ejector  system  they  do  not.  By  the 
true  beat  of  the  valves  and  the  pressure  gauge  the 
engineer  can  himself  detect  leakage  or  faulty  running 
of  his  pumps,  but  he  must  depend  upon  the  accurate 
information  of  his  inspectors  for  his  knowledge  of  the 
ejector. 

QUARTERS  FOR  STAFF. 

The  provision  of  a  house  on  the  station  grounds  is 
part  of  the  superintendent's  salary.  If  there  is  no 
lodging,  allowance  is  granted  and  he  takes  up  his  quarters 
as  close  to  the  station  as  he  can. 

It  is  of  even  more  importance  to  provide  quarters  for 
an  ejector  system  than  for  a  pumping  station.  In  addi- 
tion to  the  house  for  the  superintendent,  the  drivers, 
firemen,  and  ejector  inspectors  require  accommodation. 


94       EFFICIENCY  OF  PUMPS  AND  EJECTORS 

Every  engineer  experienced  in  his  profession  knows 
that  provision  must  be  made  for  strikes,  sickness,  and 
emergency,  and  the  more  of  his  staff  he  is  able  to  provide 
with  quarters  close  to  the  station,  the  less  he  has  to  fear 
breakdown  from  such  causes.  Again,  if  the  ejector  in- 
spectors live  two  or  three  miles  from  the  power  station, 
and  their  particular  section  is  close  to  their  homes,  it 
is  obvious  they  would  simply  waste  time  by  making  a 
double  journey  to  and  from  the  power  house  each  day 
to  report.  If  they  do  not  personally  report.,  the  superin- 
tendent will  be  out  of  touch  with  these  men  for  weeks 
at  a  time,  and  have  no  check  on  their  work. 

INSPECTION  OF  EJECTORS. 

Opinions  differ  as  to  how  often  inspection  is  necessary. 
Provided  the  ejector  is  in  good  condition,  it  will  run  for 
many  months  ;  but  to  leave  them  for  such  long  periods 
unattended  cannot  be  recommended,  if  efficiency  is 
desired.  If  the  ejector  stations  are  working  at  their  full 
capacity,  and  stoppage  for  even  a  few  hours  would  cause 
flooding  of  basements,  they  should  be  examined  once 
a  day,  especially  in  certain  countries  where  labour  is 
cheap  but  inefficient,  and  a  '  blow  through  '  may  occur 
from  some  neglect.  In  England  twice  a  week  should  be 
enough. 

SELECTION  OP  STAFF. 

With  regard  to  a  pumping  installation  of  rotary  crank 
and  flywheel  engines,  there  is  not  much  difficulty  in 
obtaining  the  services  of  a  suitable  engineer-in-charge 
as  superintendent.  Men  with  marine  experience  often 
fill  such  situations  with  credit.  They  are  accustomed  to 
exercising  authority,  and  in  most  cases  are  competent 
instructors,  besides  being  able  to  test  their  own  engines. 


STAFF:    SUPERVISING  95 

The  staff  will  respect  them,  discipline  will  be  main- 
tained, and  any  casual  visitor  to  the  station  will  notice 
that  though  the  place  is  spotlessly  clean,  the  superin- 
tendent *  appears  '  to  have  little  to  do  ! 

There  is  no  surer  sign  of  efficiency  than  the  self -running 
appearance  of  a  power  station. 

Such  men  will  be  in  possession  of  a  Board  of  Trade 
certificate,  and  able  to  return  to  sea  if  they  so  desire. 
An  engineer  in  charge  has  very  often  to  be  insistent  on 
money  being  granted  for  certain  purposes,  and  an  adequate 
remuneration  for  the  staff,  and  unless  he  is  in  a  more 
or  less  independent  position  he  may  have  to  put  up 
with  parsimony  and  inefficiency  on  every  hand. 

The  selection  of  an  ejector  staff,  from  superintendent  to 
inspector,  is  not  an  easy  matter.  In  the  first  place,  the 
engineer  must  have  a  complete  knowledge  of  the  ejectors. 

He  must  be  able  to  visualise  every  working  part,  so 
that  when  an  inspector  reports  a  fault  he  will  be  able 
to  instruct  him  precisely  what  to  do  to  prevent  its 
recurring,  as  it  will  be  quite  impossible  for  him  to  visit 
every  ejector  station  himself. 

He  must  have  tact  and  patience,  encourage  the  report- 
ing of  any  fault  or  peculiarity  in  working,  or  he  will 
never  be  informed  of  those  very  details  he  ought  to 
know.  If  once  the  inspecting  staff  are  reprimanded 
and  fined  for  reporting  faults,  he  will  never  obtain  the 
best  results  from  his  men. 

The  inconstant  human  factor  is  the  most  potent  in- 
fluence we  have  to  deal  with,  therefore  we  must  under- 
stand the  class  of  man  who  actually  supervises  the 
work.  If  you  do  not  gain  their  confidence,  you  cannot 
expect  them  to  have  confidence  in  you.  You  can  stan- 
dardise the  parts  of  an  intricate  machine,  but  you  cannot 
standardise  the  human  intellect. 


96      EFFICIENCY  OF  PUMPS  AND  EJECTORS 

The  best  plan  is  to  select  reliable  lads  of  seventeen  or 
eighteen  years  of  age,  and  explain  the  working  of  the 
ejectors  to  them.  If,  after  a  few  months  they  show 
intelligence  in  their  routine  work,  and  take  an  interest 
in  the  records,  place  them  on  the  staff,  and  draw  up 
a  scale  of  pay  advancing  each  year,  till  it  arrives  at  the 
figure  paid  to  mechanics.  At  the  same  time  inform 
them  they  will  be  entitled  to  lodging  and  the  usual 
privileges.  If  he  is  a  good  man  give  him  inducements 
to  make  it  his  permanent  work.  It  will  repay  you 
many  times  over,  as  on  these  men  the  real  efficiency 
of  the  scheme  will  depend. 

The  work  required  is  little  more  than  care  with  intelli- 
gence. If  a  skilled  mechanic  is  engaged  for  routine  work 
of  this  description,  he  will  look  down  on  it  in  a  few 
months,  and  resign.  Constant  changes  will  mean  end- 
less explaining  and  reinstructing  new  hands,  as  it  is 
quite  the  exception  to  pick  up  men  who  have  already 
had  experience  in  the  work. 

Apart  from  mere  chance,  the  ability  to  select  the  right 
man  for  a  particular  post  depends  entirely  on  the  experi- 
ence and  disposition  of  those  whose  duty  it  is  to  dis- 
criminate between  the  applicants. 

A  competent  man  will  select  competent  assistants, 
while  the  incompetent  invariably  consider  their  own 
shortcomings  and  desires  before  the  work  to  be  done. 
Talent  is  not  wanted  where  it  is  not  understood. 

Faculties  of  observation  and  record  are  the  surest 
signs  of  competency. 

Be  just,  encourage  ability,  and  judge  your  men  by  the 
work  they  do.  Bear  in  mind  the  labourer  is  worthy  of 
his  hire.  Pay  a  good  wage  to  a  good  man ;  cheap  labour 
is  by  far  the  most  extravagant  of  all  '  economies  '  in  the 
long  run.  You  cannot  drive  a  man  with  brains ;  but 


STAFF:    SUPERVISING  97 

you  can  lead  him  anywhere.  Consider  the  interests  of 
those  you  employ,  and  never  trade  on  their  privileges. 
If  they  are  entitled  to  a  day  off,  see  that  they  get  it. 
Be  large-minded  before  all  else,  eschew  meanness,  and 
do  not  lower  yourself  by  blaming  your  subordinates  for 
your  own  ignorance.  Never  chide  them  or  abuse  them 
before  others,  or  condemn  an  action  in  haste.  He  may 
be  right  and  you  may  be  wrong,  and  two  wrongs  do  not 
make  a  right.  You  cannot  expect  them  to  stand  by 
you  if  you  do  not  stand  by  them  when  the  critical  times 
come.  There  is  nothing  more  terrible  than  ignorance 
with  spurs  on.  Loyalty  of  a  staff  is  won ;  it  cannot  be 
made  to  order. 

Never  make  a  practice  of  disparaging  your  men  or 
discrediting  their  work ;  it  earns  nothing  but  contempt. 
Unless  you  have  served  your  time,  and  done  the  work 
they  are  doing,  and  know  for  example,  from  daily  experi- 
ence, why  a  flat  file  has  a  safe  edge,  and  a  twist  drill  a 
taper  shank,  depend  upon  it  they  can  give  you  points. 
Even  a  navvy  has  a  method  in  using  his  pick  and 
shovel. 

Do  not  forget  that  endurance  and  adversity  have  a 
limit. 

Avoid  giving  humilating  slights ;  there  is  nothing  so 
disastrous  to  your  own  dignity  and  prestige.  No  system, 
however  imperfect  and  unjust,  compels  non-recognition 
and  obstinate  indifference  to  merit.  Freeze  merit  out 
of  existence  and  the  cogs  of  the  administrative  machine 
rapidly  deteriorate  and  rust.  No  system  is  perfect, 
but  administration  is  the  soul  of  every  system, 
and  the  responsibility  of  a  discontented  service, 
which  is  the  basis  of  waste  and  inefficiency,  cannot 
be  evaded  by  those  who  are  entrusted  with  adminis- 
trative powers. 

G 


98       EFFICIENCY  OF  PUMPS  AND  EJECTORS 

If  you  do  not  pay  a  good  man  a  good  wage,  sooner  or 
later  you  will  lose  him. 

If  your  men  have  the  chance  of  promotion  to  a  better 
job,  assist  them  all  you  can ;  you  will  be  surprised  how 
many  good  men  you  have  on  your  staff. 

If  some  particular  work  has  to  be  done  in  a  hurry,  ask 
them  if  they  have  got  all  they  want  to  do  it.  If  they 
have  not,  see  that  they  get  it,  and  work  will  be  done  in 
record  time. 

If  you  do  not  pay  your  men  sufficient  wages  to  live 
on,  you  cannot  expect  them  to  devote  the  whole  of  their 
time  to  your  service. 

You  want  the  men  who  are  thinking  how  well  they 
can  do  the  work,  and  not  how  they  can  hang  on  to 
their  job. 

Every  post  is  worth  a  certain  sum,  plus  a  margin  for 
ability  and  responsibility.  To  fill  a  good  post  with  a 
cheap  man  simply  lowers  the  standard  of  work.  If 
men  are  increased  in  pay  solely  for  length  of  service,  all 
must  be  treated  alike.  Partiality  in  the  wages  sheet  is 
the  cause  of  more  discontent  and  friction  than  any  other 
cause. 

The  author  has  supervised  labour  of  many  nationalities, 
in  many  countries,  from  marine  engineers  and  skilled 
European  mechanics  to  African  natives  and  Arab  con- 
victs, and  human  nature  is  much  the  same  all  the  world 
over.  Eastern  races,  though  illiterate,  are  quick  to 
sum  up  the  character  and  disposition  of  their  superiors. 
They  appreciate  justice  no  less  than  the  best  European 
mechanic  appreciates  knowledge  and  ability;  and  there 
is  nothing  so  conducive  to  respect  and  discipline  as  for 
the  engineer  in  charge  to  be  a  man  of  action,  who  knows 
precisely  what  to  do  and  how  to  do  it. 

Impossible  orders  will  ruin  the  best  of  men,  and  obstinate 


STAFF:    SUPERVISING  99 

indifference  rapidly  breeds  contempt.  No  matter  what 
the  work  is, '  costs  and  efficiency  '  are  as  much  dependent, 
if  not  more  so,  on  the  working  of  the  staff  as  on  the 
most  economical  machinery.  An  inefficient  staff,  with 
indifferent  supervision,  will  be  responsible  for  wasted 
stores,  bad  repairs,  constant  friction,  and  a  hundred  and 
one  petty  troubles  which  only  those  who  have  had 
experience  can  realise. 


CHAPTER  VI 

SINKING  AND  ERECTION  OF  CAST-IRON 
TUBBINGS 

CAST-IRON  TUBBING. 

EJECTORS  may  be  placed  in  cast-iron  tubbings  or  masonry 
chambers.  For  many  reasons  the  cast-iron  tubbing  is 
to  be  preferred  in  water -logged  ground.  They  can  be 
sunk  with  compressed  air  by  means  of  the  air  lock,  after 
the  manner  of  a  bridge  caisson.  There  is  better  control 
of  the  sinking  of  the  chamber,  and  less  chance  of  danger 
to  surrounding  property  from  ground  subsidence.  The 
lead  joints  between  the  tubbing  segments  can  be  caulked 
and  recaulked  absolutely  tight,  even  after  settlement, 
and  such  chambers  can  be  sunk  beneath  the  streets  in 
restricted  areas,  with  a  minimum  of  excavation.  Pre- 
sumably the  masonry  chamber  has  a  longer  life,  but 
cast-iron  water-pipes  have  been  in  use  for  upwards  of 
a  century,  and  as  far  as  the  author  is  aware,  no  time 
limit  has  been  determined  for  the  life  of  a  cast-iron 
tubbing  under  average  conditions. 

Plate  VIII.,  page  26,  shows  a  typical  example  of  a 
cast-iron  tubbing,  sunk  in  water-logged  ground  in  a 
comparatively  narrow  street.  The  tubbing  consists  of 
cast-iron  segments,  which  are  flanged  and  bolted  to- 
gether, thus  making  a  series  of  rings,  which  are  built 
up  one  upon  the  other,  till  the  shell  is  completed. 

The  flanges  are  tapered  and  have  a  beading  cast  upon 
100 


SINKING  AND  ERECTION  101 

one  edge  ;  thus  when  two  flanges  are  drawn  together 
there  is  a  recess,  into  which  is  caulked  a  flattened  lead- 
pipe,  through  which  yarn  has  previously  been  threaded. 

MARKING  OUT  TUBBING. 

The  first  step  in  the  sinking  of  the  tubbing  is  to  mark 
out  the  exact  position  in  relation  to  the  proposed  street 
manhole,  from  which  the  effluent  will  gravitate  to  the 
ejectors. 

Iron  pegs  are  driven  into  the  ground,  or  other  suitable 
marks  made  at  a  distance  from  the  actual  site,  so  that 
lines  can  be  run  across  the  excavation  for  setting  out  the 
first  ring,  and  checking  the  work  as  it  proceeds.  The 
position  of  these  pegs  or  marks  must  be  accurately  noted, 
or  much  difficulty  may  be  experienced  later  on,  when  it 
is  desired  to  sink  the  manhole  precisely  in  line  with  the 
inlet  pipe  to  the  ejector.  A  bench  mark  must  also  be 
made  on  the  curb  or  other  suitable  spot,  the  value  deter- 
mined, and  the  level  of  the  ground  taken,  in  order  that 
the  entrance  cover  may  be  eventually  set  to  correspond 
with  the  street  macadam  or  pavement. 

SINKING  TUBBINGS. 

A  square  excavation  of  such  dimensions  as  to  leave 
room  for  timbering,  in  addition  to  the  outside  diameter 
of  the  tubbing,  is  now  carried  down  to  water  level.  In 
this  excavation  the  first  ring  is  assembled  and  carefully 
lined  up  in  position. 

This  ring  is  provided  with  a  cutting  edge,  and  on  the 
inside  of  each  segment  are  cast  the  flanges  to  which  the 
floor  is  bolted  after  the  tubbing  has  been  sunk  to  its 
correct  level.  Each  segment  has  its  correct  place,  and 
great  care  must  be  taken  in  erecting  the  first  ring  that 
the  upper  segment  through  which  the  inlet  pipe  passes 


102     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

will  come  into  its  correct  position,  in  line  with  the  man- 
hole peg,  as  the  tubbing  cannot  be  turned  when  erected. 
The  inspector  under  whose  supervision  the  work  is 
being  carried  out  must  carefully  inspect  the  plates  for 
cracks,  as  they  are  not  infrequently  fractured  in  trans- 
port and  the  crack  only  disclosed  under  water  pressure, 
when  the  tubbing  is  completed.  To  remove  a  lower 
segment  when  the  work  is  finished  is  both  a  tedious  and 
expensive  business. 

By  means  of  a  hand  crane  successive  rings  are  now 
added  to  the  one  already  in  position,  till  the  level  of 
the  cone  is  reached.  The  floor  segments  and  steel  joists 
are  now  lowered  into  the  shell,  as  they  will  not  pass 
through  the  air  lock,  and  either  rest  on  temporary  girders 
or  are  suspended  by  chains  and  shackles  to  the  flanges 
of  the  segments. 

The  delivery  main  passes  through  one  of  the  cone 
segments,  which  ring  is  next  fixed  in  place,  on  which 
again  rest  the  neck  rings  one  above  the  other.  The 
upper  neck  ring  is  provided  with  bosses  for  the  air  main 
and  exhaust  pipe  connections,  and  they  must  face  in 
the  right  direction,  as  shown  on  the  site  plan.  Finally 
the  cover  is  bolted  on,  to  which  the  air  lock  is  attached. 

Am  LOCK  FOR  SINKING  TUBBING. 

The  air  lock  consists  of  two  wrought -iron  cylindrical 
chambers,  with  dished  ends,  bolted  to  one  another  so 
as  to  form  twin  compartments.  In  one  end  of  one  com- 
partment is  a  circular  outlet,  to  which  is  riveted  a  flange 
for  bolting  to  the  tubbing  cover.  This  forms  the  base 
or  foot  of  the  air  lock.  On  the  opposite  end  or  top  are 
flanges  for  the  relief  valve  and  pressure  gauge.  In  one 
side  of  this  chamber  is  a  rectangular  opening  to  corre- 
spond with  a  similar  opening  in  the  twin  compartment, 


SINKING  AND  ERECTION  103 

which  is  also  provided  with  a  second  rectangular  open- 
ing to  the  atmosphere.  Heavy  doors  are  hinged  to  these 
openings,  and  the  two  compartments  are  of  such  dimen- 
sions that  two  men  can  stand  together  in  either  of  the 
two  chambers  when  the  partition  door  is  closed.  Assum- 
ing a  man  desires  to  enter  the  tubbing  under  pressure, 
he  climbs  into  the  air  lock  and  closes  the  door  after  him. 
He  then  opens  a  pet  cock  in  the  partition  door,  and 
permits  the  air  pressure  from  the  tubbing  to  fill  the  air 
lock  till  an  equilibrium  has  been  established.  He  then 
opens  the  partition  door,  closes  it  after  him,  and  descends 
through  the  base  of  this  chamber  by  means  of  a  rope 
ladder  to  the  bottom  of  the  tubbing.  The  air  lock  is 
now  under  pressure,  and  before  a  second  man  can  enter 
from  the  atmosphere,  he  must  relieve  the  pressure  by 
opening  the  pet  cock  to  the  atmosphere  in  precisely 
the  same  way  as  the  first  man  admitted  the  compressed 
air  from  the  tubbing  to  the  air  lock. 

SINKING  UNDER  PRESSURE. 

To  sink  the  tubbing,  the  soil  is  excavated  from  the 
bottom  and  hoisted  up  through  the  air  lock,  the  air 
pressure  being  sufficient  to  prevent  any  water  from 
entering  the  tubbing.  When  2  ft.  or  3  ft.  have  been 
excavated,  the  air  pressure  is  lowered  and  the  tubbing 
sinks.  Once  this  operation  is  started,  work  continues 
night  and  day,  as  it  is  of  importance  that  the  air  pres- 
sure should  not  be  removed  till  the  floor  is  fixed,  or  the 
sand  and  water  will  rise  up  in  the  tubbing  and  an  immense 
amount  of  re-excavation  will  have  to  be  carried  out. 

The  position  of  the  tubbing  is  determined  from  time 
to  time  with  the  level  and  staff,  the  length  of  the  cast- 
iron  plates  from  the  cover  to  the  invert  of  the  aperture 
for  the  inlet  pipe  having  been  previously  ascertained. 


104     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

While  the  tubbing  is  being  sunk  this  aperture  is  covered 
with  a  blank  flange.  By  keeping  the  staff  on  the  cover, 
and  looking  through  the  level  while  the  tubbing  is  sink- 
ing and  regulating  the  air-relief  valve,  the  invert  of  the 
inlet  can  be  brought  to  rest  exactly  at  the  predeter- 
mined level. 

To  ease  the  process  of  sinking,  it  is  a  good  plan  to  fill 
in  the  space  between  the  timbering  and  the  tubbing  walls 
with  gravel  to  a  depth  of  2  ft.  or  3.  ft.  before  sinking 
commences.  This  acts  as  a  lubricant,  and  there  is  not 
so  much  tendency  for  the  tubbing  to  '  drag  '  the  surround- 
ing soil  with  it  and  cause  local  subsidence. 

During  the  initial  stages  of  sinking,  the  tubbing  must 
be  weighted  or  the  air  pressure  is  liable  to  lift  the  whole 
shell,  with  the  result  that  the  air  will  blow  out  from  under 
the  cutting  edge,  and  the  tubbing,  which  is  top  heavy 
with  the  air  lock  in  position,  will  cant  over,  and  be  very 
difficult  to  right.  With  a  20-ft.  tubbing  even  a  pressure 
of  a  few  pounds  must  be  applied  with  care.  As  the  cone 
sinks  the  earth  is  filled  in  and  the  weights  are  removed. 

Whether  the  tubbing  is  sunk  with  compressed  air  or 
by  hand  excavation  and  steam  pumps,  great  care  must 
be  exercised  to  see  that  the  filling  takes  place  before  the 
floor  is  caulked  and  made  water-tight,  as  the  chamoer 
is  buoyant  and  will  float  up,  which  will  cause  a  heavy 
inrush  of  sand  beneath  the  floor  plates  and  undermine 
the  nearest  house  foundations. 

Provided  the  tubbing  maintains  a  vertical  position 
during  sinking,  and  only  has  to  withstand  an  even  pres- 
sure, there  is  ample  strength  ;  but  it  is  easy  to  fracture 
the  plates  if  the  shell  is  squeezed  unequally,  or  great 
pressure  is  brought  to  bear  locally  in  attempting  to  right 
a  tubbing  that  has  canted  over.  At  this  stage  the  prin- 
cipal trouble  is  the  tendency  of  the  tubbing  to  sink  too 


SINKING  AND  ERECTION  105 

far  into  the  sand.  If  the  air  pressure  is  released  by 
accident  from  the  bursting  of  a  pipe  or  a  joint  failing, 
the  shell  will  sink  4  ft.  or  5  ft.,  and  there  is  no  means  of 
stopping  it.  At  the  same  time  the  sand  will  rise  up  from 
the  bottom, and  the  whole  interior  have  to  be  re-excavated. 
The  tubbing  can  be  raised  by  air  pressure  and  hydraulic 
jacks  ;  but  it  is  a  delicate  and  tedious  business,  as  suffi- 
cient air  pressure  for  this  purpose  is  invariably  sufficient 
to  start  a  bad  '  blow  through  '  in  soft,  water-logged  soil. 
Through  sandy  soil  or  fine  gravel  the  tubbing  sinks 
very  easily,  but  when  stiff  clay  beds  are  met  with,  it  is 
often  necessary  to  make  a  special  platform  to  rest  on 
the  lugs  cast  on  the  outside  of  the  cone  for  the  purpose, 
and  pile  it  high  with  scores  of  sandbags.  If  the  clay 
bed  is  dry  and  hard,  and  only  becomes  wet  round  the 
tubbing  from  the  subsoil  water  forcing  its  way  up,  the 
shell  will  be  held  in  a  vice -like  grip,  and  will  not  sink 
without  external  excavation. 

TUBBING  FLOOR,  FIXING  IN  PLACE. 

With  the  sinking  of  the  shell  to  the  required  depth,  the 
next  operation  is  to  fix  the  floor,  still  under  air  pres- 
sure .  The  segments  are  lowered  on  to  the  sand,  assembled 
together,  and  drawn  up  to  the  flanges  provided  for  the 
purpose  on  the  bottom  ring.  Care  must  be  taken  that 
the  flanges  of  these  floor  segments  are  drawn  evenly 
together,  or  unequal  strains  are  liable  to  be  set  up, 
which  will  cause  fracture  when  the  equilibrium  between 
the  internal  air  pressure  and  the  subsoil  water  is  destroyed 
by  removing  the  air  lock. 

In  this  class  of  tubbing  the  flanges  of  the  segments 
are  not  machined,  and  it  will  readily  be  understood  that, 
owing  to  the  lead  joints,  the  whole  tubbing  is  more  or 
less  flexible,  and  depends  upon  its  rigidity  for  the  external 


106     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

pressure.  When  the  internal  pressure  is  removed  settle- 
ment of  the  plates  will  occur,  as  the  whole  cylinder  is 
subject  to  external  pressure  alone.  The  strength  of  a 
circular  shell,  under  an  even  external  pressure,  is  well 
known,  but  with  local  strains  flanges  are  easily  frac- 
tured. The  floor  should  remain  perfectly  water-tight 
after  the  air  lock  has  been  removed  for  twenty-four  hours 
(that  is  to  say,  under  atmospheric  pressure),  with  bolts 
tightened  up,  joints  caulked,  and  steel  joists  firmly 
wedged  in  position,  as  the  subsoil  takes  some  hours 
before  it  exerts  its  full  pressure.  This  is  probably  due 
to  the  compressed  air  forcing  the  water  through  the 
sand — that  is  to  say,  the  soil  is  comparatively  dry  round 
the  tubbing  while  the  sinking  is  in  progress  under  air 
pressure. 

It  must  always  be  borne  in  mind  that  the  floor  is  under 
great  pressure,  and  it  is  by  no  means  infrequent  for  a 
rib  or  flange  to  split  if  the  metal  is  not  perfectly  sound. 
With  a  cracked  segment  there  is  nothing  for  it  but  to 
replace  it.  Finally,  the  floor  is  filled  with  concrete 
rendered  over  in  such  a  way  as  to  drain  to  a  small 
sump  left  in  the  concrete,  and  the  tubbing  is  ready 
for  the  ejectors. 

SETTING  EJECTORS  IN  POSITION. 

There  is  no  necessity  to  bolt  the  ejectors  to  the  floor. 
They  must  be  set  level,  and  the  base  packed  up  till  the 
inlet  pipe  and  the  deli  very  pipe  come  in  line  with  their 
respective  apertures  in  the  walls  of  the  tubbing,  when 
they  are  grouted  up.  The  internal  bell  weight  must 
hang  truly  in  place,  and  the  bracket  supporting  the 
external  lever  fulcrum  adjusted  to  such  a  position  that 
the  bell-rod  passes  freely  through  the  crown  of  the 
ejector  without  any  tendency  to  seize. 


SINKING  AND  ERECTION  107 

When  red  lead  is  used  for  jointing  the  cover,  it  should 
not  be  permitted  to  squeeze  out  of  the  joint,  as  it  will 
harden  and  foul  the  top  bell  float.  In  some  types  of 
ejectors  there  is  very  little  clearance.  All  rods,  washers, 
nuts,  etc.,  in  contact  with  the  fluid  must,  without  excep- 
tion, be  of  gun  metal.  The  point  to  remember  is  that 
the  action  of  the  bell-rod  must  be  perfectly  free  with 
a  minimum  of  friction. 

When  the  ejectors  have  been  put  together  they  should 
be  filled  with  water,  and  at  least  the  working  air  pres- 
sure applied,  to  ascertain  if  all  the  joints  are  tight.  No 
leakage  whatever  should  be  permitted,  and  if  air  comes 
from  the  exhaust  outlet,  when  the  air  valves  are  open, 
the  exhaust  valves  should  be  refaced.  Needless  to  say, 
the  exhaust  stop  valves  must  be  wide  open  when  testing. 

EJECTOR  INLET  PIPE. 

In  Plate  VIII.,  page  26,  it  will  be  noticed  the  inlet  pipe 
passes  through  the  wall  of  the  tubbing.  A  better  arrange- 
ment is  for  the  ejector  pipe  to  terminate  in  a  spigot, 
leaded  into  a  socket  and  flange,  and  this  flange  will  bolt 
on  to  a  boss  on  the  inside  of  the  tubbing.  A  boss  sunk 
into  the  segment  on  the  outside  will  enable  the  pipe 
from  the  tubbing  to  the  inlet  manhole  to  be  entirely 
separate.  The  exterior  boss  must  in  no  way  stand  out 
from  the  tubbing  or  it  will  impede  sinking.  If  much 
settlement  occurs  when  the  inlet  passes  through  the 
tubbing,  it  is  liable  to  snap  off,  and  can  only  be  replaced 
at  much  expense . 

TUBBING  SINKING  BY  PUMP  OB  GRAB. 

If  no  buildings  are  near  the  proposed  site  of  a  tubbing, 
and  the  soil  is  fairly  stiff,  it  is  cheaper  and  quicker  to 
sink  by  hand  excavation  and  a  steam  pump,  as  the  men 


108     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

can  work  in  daylight  and  are  not  hampered  by  the  air 
lock  in  getting  rid  of  the  spoil. 

A  third  way  is  to  excavate  with  a  steam  grab,  and  not 
pump  out  the  water  till  it  is  desired  to  fix  the  floor,  but 
in  this  method  any  stone  or  obstruction  under  the  cutting 
edge  of  the  bottom  ring  will  cause  the  tubbing  to  cant 
over  and  sink  unevenly.  There  is  no  economy  in  this 
method  over  the  steam  pump. 

BRICK  CHAMBERS. 

In  the  case  of  circular  brick  chambers,  they  must 
either  be  built  up  from  the  bottom  or  sunk  like  a  well  by 
excavating  the  interior  soil  and  building  the  masonry 
on  the  top,  while  the  water  is  kept  down  by  pumping. 
But  the  great  objection  to  the  use  of  steam  pumps  is 
the  heavy  subsidence  of  the  surrounding  ground  which 
invariably  takes  place.  If  divers  can  be  obtained  to 
work  in  the  depth  of  water  that  exists,  no  pumping  is 
required,  and  the  floor  is  made  by  filling  the  bottom 
with  concrete,  and  finally  grouting  with  liquid  cement 
distributed  by  vertical  pipes,  previously  fixed  for  the 
purpose. 

Such  chambers  must  be  of  substantial  construction, 
and  the  crown  may  be  corbelled  in  or  arched  over  ;  but 
they  cannot  be  guaranteed  water-tight  in  the  sense  of 
having  a  perfectly  dry  internal  surface  on  which  neither 
seepage  nor  moisture  can  be  detected  ;  but  if  carefully 
built  with  the  best  materials  will  answer  their  purpose  in 
certain  situations.  The  only  method  of  making  a  brick 
chamber  of  this  description  perfectly  water-tight  is  by 
lining  it  with  bitumen,  with  an  internal  lay  of  masonry. 
But  it  is  necessary  to  lay  the  material  on  a  dry  surface. 
If  it  is  laid  on  a  cement  surface  under  constant  seepage 
the  pressure  will  force  it  off. 


SINKING  AND  ERECTION  109 

TESTING  TUBBINGS  AND  BRICK  CHAMBERS. 

It  is  not  proposed  to  go  into  the  matter  of  specifica- 
tions, but  it  may  be  said  the  contractor  should  be  held 
responsible  for  handing  over  the  tubbing  and  ejectors 
complete  in  every  detail,  in  a  perfectly  water-tight  con- 
dition, as  specified  and  described,  and  the  test  to  which 
these  chambers  should  be  subjected  is  their  ability  to 
withstand  the  pressure  of  the  subsoil  water  for  one 
year  without  leakage.  Some  settlement  may  take  place 
as  subsoil  water  invariably  differs  in  level  according 
to  the  season  of  the  year.  It  is  not  unusual  to  retain  a 
small  percentage  of  the  contractor's  price  till  the  con- 
ditions have  been  fulfilled. 

AIR  COMPRESSED  FOR  SINKING  TUBBINGS. 

From  10  Ib.  to  12  Ib.  air  pressure  will  be  found  suffi- 
cient for  ordinary  street  work  ;  but  when  ejector  tubbings 
are  sunk  60  ft.  and  70  ft.  for  draining  the  sludge  from 
sewage  sumps,  a  greater  pressure  is  required.  When 
the  air  pressure  is  first  applied,  it  will  be  found  that  it 
takes  a  higher  pressure  to  expel  the  water  than  it  does 
to  keep  it  from  flowing  into  the  tubbing. 

Portable  steam  air-compressors  are  to  be  preferred 
for  air-lock  work ;  they  are  the  most  reliable,  will  run 
at  a  slow  speed,  and  do  not  cause  pulsations  in  the 
chamber,  which  react  on  the  ear-drums  with  unpleasant 
effect.  Again  small  internal-combustion  engines  can 
hardly  be  relied  upon  to  run  for  three  or  four  weeks 
continuously. 

On  the  other  hand,  there  is  little  room  in  narrow 
streets  for  operating  such  machinery,  as  it  will  consist 
of  a  horizontal  flywheel,  tandem  compressing  engine, 
mounted  on  a  four-wheeled  carriage,  with  another 
carriage  for  a  10  horse  -  power  steam  boiler,  with  its 


110    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

coal  and  water  receptacles.  It  is  also  expensive,  and 
unless  more  than  one  portable  unit  is  provided,  only 
one  tubbing  can  be  sunk  at  a  time. 

There  is,  however,  no  reason  why  the  permanent  air 
main  should  not  be  laid  first  and  a  temporary  stationary 
compressor  plant  put  down  by  the  contractor,  so  that 
several  tubbings  can  be  sunk  at  once,  and  the  trans- 
portation of  machinery  about  the  city  is  done  away 
with. 


CHAPTER  VII 

EJECTOR  AND  AIR-MAIN  FAULTS  AND 
REMEDIES 

As  previously  remarked,  the  pneumatic  ejector  is,  com- 
paratively speaking,  an  obscure  apparatus  compared 
to  a  pump.  There  are  a  few  records  of  its  merits,  but 
none  of  its  failings,  and  no  reference  work  to  which  the 
Borough  Engineer  can  turn  for  information  on  its  daily 
working  or  when  he  has  to  consider  the  drainage  of  a 
new  area,  or  remodel  an  existing  system.  Manufac- 
turers' catalogues  and  special  articles  in  the  technical 
Press  naturally  confine  their  remarks  and  descriptions 
to  the  merits  of  the  apparatus  they  wish  to  sell,  and 
those  simple  precautions  in  erection,  supervision,  and 
maintenance,  which  make  all  the  difference  between  satis- 
faction and  disappointment,  are  not  disclosed.  Indeed, 
in  nine  cases  out  of  ten,  the  designer  and  manufacturer 
are  not  aware  of  their  existence. 

What  is  understood  is  invariably  selected  in  place  of 
what  is  not  understood,  and  ejectors  have  often  been 
'  turned  down '  in  preference  to  a  pump  for  the  sole 
reason  that  unknown  difficulties  which  the  ordinary 
pump  attendant  may  not  be  able  to  correct,  might  jeopar- 
dise the  success  of  the  scheme.  The  very  simplicity  of 
the  apparatus  arouses  suspicion,  as  if  the  ejector  stops, 
there  is  often  nothing  to  indicate  the  reason,  and  the 
attendant  must  know  how  to  locate  the  cause  without 

dismantling  the  whole  machinery. 

111 


112     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

Sometimes  it  is  easier  to  express  the  merits  of  a  system 
by  pointing  out  the  failings  to  which  it  is  subject.  The 
engineer  is  then  in  a  position  to  draw  his  own  conclu- 
sions as  to  whether  such  failings  are  of  such  a  nature 
as  to  counterbalance  the  obvious  advantages.  There  is 
more  to  be  learnt  from  careful  records  of  what  to  avoid 
than  from  an  able  summary  of  an  apparatus  in  perfect 
working  order.  It  is  for  this  reason  that  it  is  now  pro- 
posed to  describe  some  of  the  faults  and  failings  of 
ejectors,  air  mains,  and  their  accessories,  together  with 
those  precautions  which  should  be  taken  to  avoid  sub- 
sequent expense. 

CAUSES  OF  EJECTORS  STOPPING. 

There  is  no  limit,  practically  speaking,  as  to  how  long 
an  ejector  will  go  on  working. 

The  leathers  of  the  inlet  and  discharge  valves  will 
be  the  first  to  fail ;  but  with  good  material  a  life  of 
several  years  is  not  too  much  to  expect.  When  ejectors 
are  found  stopped,  it  is  nearly  always  from  some  easily 
preventable  cause  or  neglect  in  erection  or  attendance. 

For  instance,  the  set  screw  holding  the  exterior  balance - 
weight  to  the  lever  may  jar  loose  if  not  tight,  and  the 
same  may  be  said  for  the  set  screw  which  holds  the 
slide-valve  lever  pin  to  the  lever. 

With  ejectors  that  are  fitted  with  flat  weights,  solids 
may  rest  thereon  as  the  water  recedes.  This  may 
prevent  the  weight  rising  in  due  course  for  the  admis- 
sion of  the  air  when  the  ejector  is  full. 

Grease  and  dirt  may  accumulate  after  a  time  in  the 
automatic  valves,  or  choke  the  control  pipes,  and  so 
prevent  the  valves  from  being  thrown  over. 

Fracture  and  breakage  or  worn-out  mechanical  parts 
are  practically  unknown,  and  that  is  why  leather 


FAULTS  AND  REMEDIES  113 

forms    the   only   important    item   in  the    maintenance 
sheet. 

SILENCING  CHAMBER  FOR  EXHAUST. 

If  the  3-in.  or  4-in.  exhaust  pipe  from  the  ejector  is 
permitted  to  discharge  direct  to  the  atmosphere  the 
resulting  noise  will  disturb  the  surrounding  inhabitants — 
in  fact,  much  in  the  same  way  as  the  exhaust  from  a  gas 
engine — therefore  some  form  of  silencer  is  required. 

When  an  underground  silencing  chamber  is  provided 
into  which  the  exhaust  discharges  before  escaping  by  a 
vertical  column,  care  must  be  taken  to  keep  this  chamber 
free  of  water  by  a  drain  of  not  less  than  2  ins.  in  diameter. 
If  this  is  not  done  water  will  accumulate  in  the  silencing 
chamber,  and  the  exhaust  air,  unable  to  escape,  will 
prevent  the  ejector  filling.  If  the  ejector  does  manage 
to  get  a  discharge,  the  water  will  be  observed  coming 
out  of  the  top  of  the  column. 

BLOW  THROUGH. 

If  the  balance  weight  shifts  its  position  on  the  lever, 
or  other  similar  preventable  mishap  takes  place,  the 
ejector  will '  blow  through,'  and  this  will  stop  the  ejectors 
working,  but  it  is  known  at  once  at  the  power  house. 
Again,  an  ejector  may  '  blow  through  '  and  continue 
working  from  either  the  inlet  flap  valve  being  held  open 
by  long  sticks  or  bricks,  or  by  the  delivery  valve  being 
held  open  in  the  same  manner.  In  the  former  case  the 
water  blows  back  into  the  inlet  manhole  and  is  easily 
detected ;  in  the  latter  case  the  ejector  is  filled  from  the 
rising  main  by  the  water  it  has  just  discharged — that  is 
to  say,  it  is  perpetually  discharging  the  same  water. 
This  again  is  easily  detected  by  the  inspector,  from  the 
large  number  of  strokes  the  ejector  counter  has  recorded, 

H 


114    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

Valve -face  leathers  that   have  perished  and  not   been 
replaced  will  often  be  detected  in  the  same  way. 

With  large  ejectors  discharging  city  sewage  these 
faults  are  extremely  rare — once  perhaps  in  a  number  of 
years — but  they  are  not  uncommon  when  extensive 
sewer  construction  is  in  progress,  and  the  ejectors  are 
used  to  keep  the  excavation  dry  for  sewer  laying.  In 
spite  of  orders  and  instructions,  every  article,  from  drain 
stoppers,  masons'  trowels,  and  even  iron  buckets,  have 
been  removed  from  ejectors  under  such  conditions. 

SAND  AND  STONES  IN  EJECTORS. 

If  the  ejectors  are  only  working  at  a  minimum  pres- 
sure, road  metal  may  accumulate  in  the  base  and  inter- 
fere with  the  descent  of  the  weight. 

In  the  same  way  when  draining  excavation  trenches 
it  is  possible  for  liquid  clay  and  sand  to  fill  up  the  ejector, 
when  it  is  not  surprising  the  balance  weight  fails  to 
operate. 

CHOKING  OF  EJECTORS. 

With  large  sizes  it  is  unknown.  With  small  sizes 
it  is  a  constant  nuisance  if  the  ejector  is  dealing  with 
much  refuse,  garbage,  etc.  In  such  situations  it  is  far 
better  to  erect  one  medium  size  ejector  than  a  pair  of 
small  ones.  In  situations  where  ejectors  do  not  take 
refuse,  the  small  sizes  are  no  doubt  as  reliable  as  the 
larger  ones. 

FLOATING  MATTER. 

In  localities  where  ejectors  take  the  effluent  from 
factories,  special  causes  of  obstruction  sometimes  occur. 
For  instance  an  excessive  accumulation  of  grease  in  the 
crown  of  the  ejector  will  prevent  the  float  rising,  and 


FAULTS  AND  REMEDIES  115 

cases  have  been  known  where  ejectors  have  gradually 
become  full  of  corks  and  cotton  waste. 

Though  the  ejector  will  effectually  expel  suspended 
matter  and  solids  at  each  discharge,  the  lever  should  be 
occasionally  held  down  to  get  rid  of  the;  lighter  matter, 
if  there  is  reason  to  believe  an  excessive  quantity  exists. 
Small  corks  and  similar  very  light  articles  will  at  times 
be  drawn  up  with  the  exhaust  air  into  the  piston  valves. 
There  is  a  strainer  fixed  in  the  exhaust  pipe,  close  to 
the  body  of  the  ejector,  to  prevent  this,  but  the  sudden 
shock  of  the  exhaust  will  displace  it  if  not  very  firmly 
fixed.  In  the  same  way  moisture,  grit,  and  dirt  will 
also  be  drawn  up,  and  it  is  the  exhaust  valve  from  which 
most  of  the  leakage  occurs.  Therefore,  if  the  ejectors 
are  very  slow  in  discharging,  there  is  a  higher  percentage 
of  leakage  from  this  cause.  They  should  be  examined 
every  few  months,  to  see  if  any  serious  pitting  of  the 
valve  face  has  taken  place. 

LEAKAGE  THROUGH  SLIDE-VALVE  Box. 

When  the  ejector  is  blowing  off,  air  leakage  can  some- 
times be  detected  from  the  slide-valve  box.  This  is  as 
a  rule  caused  by  ill-fitting  piston- valve  leathers,  which 
allow  the  air  to  pass  into  the  control  pipes.  Or  some- 
times grit  will  be  found  lodged  under  the  slide  valve  or 
a  burr  formed  by  the  lever  on  the  valve  seat.  Once  a 
month  all  cup  leathers,  slide  valves,  piston  valves,  and 
ejector  valves  should  be  examined. 

EXAMINATION  OF  EJECTOR  VALVES. 

It  must  be  remembered  that  though  ejector  inlet  and 
outlet  valve  boxes  have  to  be  examined  by  the  small 
inspection  cover  provided  for  the  purpose,  it  is  by  no 


116    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

means  so  objectionable  as  examining  the  interior  of  a 
pump  drawing  from  a  sump. 

Firstly,  because  before  removing  the  cover  the  ejectors 
can  be  completely  blown  out  by  holding  down  the  exterior 
balance  weight,  and  secondly,  there  is  no  collection  of 
sewage  to  putrefy.  That  is  to  say,  the  ejector  always 
keeps  the  sewers  dry ;  thus  the  sewage  is  always  fresh 
and  decomposition  has  not  had  time  to  set  in. 

STOPPING  EJECTORS. 

To  stop  an  ejector  the  inlet  valve  should  always  be 
closed  and  opened  to  its  fullest  extent  when  working,  as 
heavy  articles  and  refuse  may  lodge  in  the  groove  of 
the  sluice-valve  body. 

FALSE  DISCHARGES. 

When  ejectors  have  been  at  rest  and  the  manhole  has 
become  nearly  full — that  is  to  say,  when  there  exists  a 
'  head  '  on  the  inlet — some  types  are  liable  to  have  the 
internal  weight  raised  by  the  violent  inrush  of  water, 
so  that  the  ejector  discharges  when  it  is  only  one -third 
full — that  is,  it  will  make  a  number  of  false  discharges. 
The  result  is  a  great  waste  of  air,  as  it  will  take  a  very 
much  longer  time  to  regain  normal  levels. 

When  starting  an  ejector  under  such  conditions,  it 
is  always  prudent  to  regulate  the  first  discharge  with  the 
inlet  sluice  valve.  If  the  internal  weight  happens  to  be 
ill -balanced  with  the  external  weight,  this  fault  may  cause 
a  lot  of  trouble,  but  it  is  very  easy  to  detect  and  remedy 
by  one  familiar  with  the  apparatus. 

VENTILATION  OF  TUBBING. 

An  ejector  tubbing  or  well  should  always  be  provided 
with  an  air  scavenging  pipe  as,  like  all  underground 


FAULTS  AND  REMEDIES  117 

chambers,  dampness  cannot  be  avoided,  and  the  con- 
densation of  the  atmosphere  on  the  exhaust  pipes,  owing 
to  the  cooling  of  the  expanding  air,  keeps  the  machinery 
in  a  dripping  condition.  In  hot  climates  an  unbearable 
atmosphere  to  work  in  would  exist  without  these  pipes. 
In  very  cold  climates  precautions  have  to  be  taken 
against  freezing,  as  if  ice  forms  in  the  valve  ports  the 
pistons  will  not  throw  over. 

PAINTING  MACHINERY. 

Too  much  stress  cannot  be  laid  on  the  importance  of 
painting  the  interior  of  a  cast-iron  tubbing  and  the 
machinery  it  contains  ;  but  this  must  be  done  in  the 
first  place  before  the  cover  is  placed  in  position  and  the 
ejectors  used. 

Once  used,  the  interior  is  never  free  from  condensa- 
tion water.  There  are  several  excellent  anti-corrosive 
fluids  or  paints  on  the  market,  and  the  interior  of  the 
tubbing  should  be  painted  white,  soon  after  sinking, 
when  it  has  become  perfectly  dry.  All  ironwork  as 
soon  as  it  is  erected  should  also  receive  two  coats  after 
having  been  carefully  scraped.  If  this  work  is  left  till 
the  ironwork  is  once  rusted  and  pitted  the  paint  will 
invariably  peel  off,  and  the  lighter  sections  of  the  wrought- 
ironwork,  like  J-in.  piping  and  ladder  rungs,  will  in  a 
few  years  completely  perish.  In  the  erection  of  the 
machinery  all  bolts,  sluice- valve  gates,  spindles,  and  such- 
like items  must  be  greased  before  they  are  put  together, 
or  hours  of  labour  will  be  lost  in  wrestling  with  immov- 
able valves  and  rusted  studs. 

ENTRANCE  COVERS  TO  TUBBINGS. 

An  ejector  tubbing  is  as  a  rule  sunk  directly  beneath 
the  street,  therefore  it  is  necessary  to  provide  a  very 


118     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

heavy  form  of  iron  cover  to  withstand  the  traffic.  It 
is  hardly  practicable  to  make  these  covers  water-tight, 
as  they  frequently  have  to  be  opened,  and  owing  to  their 
great  weight  cannot  be  a  close  fit.  Any  suggestion  of 
sticking  must  be  avoided. 

Owing  to  the  surface  water  finding  its  way  between  the 
cover  and  the  frame,  it  is  difficult  to  keep  the  machinery 
in  a  clean  state. 

However,  in  nine  cases  out  of  ten,  there  seems  to  be 
no  reason  why  the  tubbing  should  not  be  so  situated 
that  the  entrance  cover  could  be  placed  on  a  street 
island  or  central  foot  walk,  in  which  case  a  light  type 
of  cover  could  be  used,  and  a  great  deal  of  the  deteri- 
oration of  the  wrought -ironwork  such  as  staging  and 
ladders  avoided.  Again,  it  dispenses  with  a  third  hand 
necessary  for  inspection.  When  large  valve  covers  have 
to  be  taken  off,  it  takes  two  men  to  handle  them,  and 
if  the  entrance  is  in  the  centre  of  a  busy  street,  as  it 
often  is,  it  takes  a  third  hand  to  guard  the  opening. 

To  arrange  the  inlet  manhole  and  the  entrance  cover 
of  the  tubbing  so  that  the  cover  is  a  few  inches  above 
the  street  level,  such  as  on  a  pavement,  is  just  one  of 
those  small  items  which  cost  nothing  extra  in  construc- 
tion but  are  the  means  of  saving  hundreds  of  pounds 
in  maintenance  in  years  to  come. 

REFLUX  VALVES. 

The  reflux  valves  on  the  rising  main  should  always  be 
placed  in  an  accessible  chamber  and  not  buried  beneath 
the  macadam.  And  here,  again,  if  the  cover  of  this 
chamber  is  placed  on  the  footwalk  expense  will  be  saved 
in  construction  and  maintenance.  It  is  not  always  pos- 
sible to  arrange  for  this  chamber  in  the  most  suitable 
place  for  inspection  purposes  ;  but  when  such  valves  are 


FAULTS  AND  REMEDIES  119 

placed  beneath  the  streets,  without  means  of  access, 
the  asphalt  or  wood  paving,  or  whatever  the  surface  may 
be,  has  to  be  broken  up  and  the  cost  of  relaying  debited 
to  the  maintenance  of  the  ejectors,  but  with  a  remov- 
able cover  no  expense  is  involved.  Some  engineers  do 
not  consider  them  a  necessity,  but  they  are  a  valuable 
safeguard  against  the  ejector  discharging  the  same  water 
over  and  over  again  when  the  delivery  valve  does  not 

close  properly  owing  to  some  obstruction. 

i 

Am  VALVES  IN  TUBBING. 

Whatever  the  particular  type  the  ejector  may  be,  it  is 
highly  desirable  that  the  automatic  air  valves  should  be 
placed  in  the  neck  of  the  chamber  as  high  up  as  possible. 
If  this  is  not  done  and  the  manhole  from  any  cause 
becomes  full  of  water,  such  as  in  the  case  of  a  burst 
water  main  or  extraordinary  floods,  these  valves  will 
become  full  of  water.  The  water  passes  up  the  air 
pipe  from  the  ejector  into  the  valves,  and  instead  of  the 
ejectors  being  able  to  work  at  their  maximum  speed 
when  they  are  most  required,  their  action  will  be  delayed 
from  this  cause,  not  only  by  water,  but  by  floating 
matter  which  may  completely  choke  up  the  small 
control  pipes.  Again,  if  the  valves  are  placed  close  to 
the  body  of  the  ejector  they  are  easily  submerged  in 
times  of  flood,  and  the  ejector  cannot  be  started  till  the 
tubbing  is  baled  out. 

UNDERGROUND  OBSTRUCTION. 

In  every  city,  it  must  be  borne  in  mind,  much  of  the 
'  underground  space  '  is  occupied  by  water  mains,  gas 
pipes,  electric  cables,  telephones,  etc.,  and  in  the  actual 
marking  out  of  the  ejector  station,  in  spite  of  informa- 


120     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

tion  and  site  plans,  the  discretion  of  the  engineer  has  to 
decide  the  most  suitable  position. 

When  possible  it  is  desirable  to  avoid  the  expense  of 
diverting  pipes  already  in  position,  but  the  best  posi- 
tion for  the  tubbing  should  not  be  sacrificed  for  such 
reasons.  A  few  extra  feet  to  the  length  of  the  inlet  pipe 
from  the  manhole  to  the  ejector  is  of  no  consequence  to 
its  efficient  working. 

Disc  VALVES. 

The  manhole  end  of  the  inlet  pipe  to  the  ejector  should 
always  be  provided  with  a  disc  valve  and  a  long  rod 
reaching  up  to  within  a  few  inches  of  the  cover,  especially 
with  small  ejectors,  owing  to  their  being  more  liable  to 
be  choked  with  refuse  when  they  stop  working  for  want 
of  water  and  the  manhole  fills  up. 

Under  such  conditions  it  is  first  necessary  to  close  the 
inlet  pipe,  and  this  can  only  be  done  by  means  of  the 
disc  valve  and  rod  in  the  manhole.  It  is  obvious,  if  the 
cover  in  the  inlet  pipe  in  the  tubbing  is  opened  before 
this  valve  has  been  let  down,  the  chamber  would  be 
flooded  with  sewage.  With  large  ejectors  the  necessity 
for  this  operation  may  never  occur,  but  it  is  one  of  those 
precautions  in  erection  that  should  never  be  omitted. 

Am  MAINS. 

The  efficiency  of  an  ejector  system  largely  depends  on 
the  care  with  which  the  air  mains  are  laid  and  tested. 
Too  much  care  cannot  be  expended  on  efficient  super- 
vision in  caulking  the  joints  and  *  bedding '  the  pipes 
on  trench  bottom,  and  not  on  filling  as  is  often  done. 

Extra  money  spent  on  construction  means  less  money 
spent  on  repairs  and  maintenance.  There  is  no  section 


FAULTS  AND  REMEDIES  121 

of  the  work  which  may  prove  so  expensive  in  main- 
tenance if  badly  carried  out. 

Leakage  from  the  air  mains  is  indeed  considered  to 
be  the  greatest  objection  to  an  ejector  system,  but  at 
the  low  pressure  maintained  there  is  no  reason  why  this 
should  be  excessive  or  amount  to  such  a  figure  as  to 
destroy  the  value  of  the  whole  system. 

It  is  true  a  large  volume  of  air  will  escape  from  an 
exceedingly  small  hole,  but  before  the  mains  are  covered 
in  it  is  easy  to  detect  and  easy  to  remedy. 

It  is  expensive  to  excavate  and  recaulk  pipes,  but 
this  should  only  be  done  if  the  leakage  exceeds  a  certain 
percentage  of  the  whole  volume  compressed.  Below 
a  certain  figure  the  extra  cost  of  maintaining  the  pipes 
'  air-tight '  would  not  balance  the  saving  in  fuel.  The 
higher  the  cost  of  fuel  the  more  economical  it  is  to  spend 
money  on  maintenance.  If  fuel  could  be  purchased  at 
a  very  cheap  rate,  say  15s.  per  ton,  it  would  not  pay  to 
keep  leakage  down  to  2  per  cent,  or  3  per  cent. 

Usually  a  10  per  cent,  loss  is  looked  upon  as  good 
enough  for  a  35  per  cent,  efficiency  over  the  whole  system. 
At  22  Ibs.  pressure  it  is  quite  possible  to  maintain  a 
5  per  cent,  loss  only,  and  with  expensive  fuel  it  pays 
to  do  it. 

LAYING  AIR  MAINS. 

At  first  sight  there  would  not  appear  to  be  many  diffi- 
culties to  contend  with  in  laying  a  cast-iron  spigot  and 
socket  pipe  a  few  feet  below  the  surface.  In  open 
ground  there  are  not,  but  when  it  comes  to  crowded 
cities,  with  narrow  streets  and  subsoil  obstructions  of 
every  description,  it  is  a  matter  of  deciding  equally 
awkward  alternatives  on  the  spot,  as  to  which  is  the 
best  line  to  take  and  least  expensive.  Air  mains  must 


122     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

be  laid  so  that  they  can  be  excavated  at  any  time.  It 
is  no  use  laying  them  under  tram  lines,  or  in  such  close 
proximity  to  stone  walls  and  other  pipes  that  the  joints 
cannot  be  recaulked.  It  should  not  be  overlooked  there 
may  be  no  indication  on  the  surface  of  the  street  of 
what  is  underneath,  and  a  hundred  or  two  hundred 
yards  of  trench  must  be  marked  out  and  opened  up  at 
a  time,  and  the  whole  trench  may  have  been  excavated 
before  it  is  found  that  the  particular  line,  which  may  be 
between  a  foot  walk  and  a  tram  line,  is  already  occupied 
by  a  water  main  or  other  pipe. 

When  any  doubt  exists  the  best  plan  is  to  keep  two 
or  three  men  sinking  trial  holes  on  the  proposed  line  well 
ahead  of  the  work.  In  old  cities  it  is  often  exceedingly 
difficult,  if  not  impossible,  to  obtain  complete  drawings 
of  the  exact  position  of  what  has  already  been  laid 
beneath  the  streets. 

Again,  new  streets  and  new  alignments  of  old  streets 
are  constantly  taking  place.  Private  roads  are  con- 
verted into  public  streets,  and  unrecorded  cesspools, 
cellars,  foundations,  and  similar  obstructions  are  inces- 
santly met  with  and  have  to  be  circumvented  by  the 
ingenuity  of  the  inspector. 

Estimates  and  specifications  only  provide  bends  that 
can  be  indicated  on  site  plans,  and  cast-iron  pipes  must 
be  laid  more  or  less  in  a  straight  line  ;  without  special 
bends,  work  may  be  hung  up  or  have  to  be  relaid. 

As  a  rule,  cast-iron  pipes  are  quoted  for  by  the  yard 
or  metre,  laid  in  place  with  a  certain  minimum  cover. 
However,  as  the  work  proceeds  it  is  invariably  found 
that  contractors  claim  extras,  as  it  is  often  not  possible 
to  lay  the  pipe  with  the  stipulated  cover  owing  to  their 
having  to  dip  under  water  mains  and  other  systems 
already  in  position. 


FAULTS  AND  REMEDIES  123 

Again,  curbstones  have  to  be  moved,  foundations 
cut  through,  supports  built  in,  old  culverts  crossed, 
and  special  protection  taken  for  the  pipes  having  to 
pass  under  railways.  If  the  specification  is  not  very 
precise,  and  the  rates  clear,  such  extras  will  amount  to 
a  large  figure  in  the  monthly  certificate. 

A  gang  of  pipe -layers  consisting  of  eighty  men,  in- 
cluding lead-runners  and  caulkers,  besides  all  necessary 
labour  employed  on  such  work,  will  lay  as  much  as 
100  yards  of  6-in.  spigot  and  socket  pipe  per  day — that 
is,  excavation,  laying,  and  jointing  and  refilling  with  a 
2  ft.  9  in.  '  cover.'  This  would  be  on  the  footwalk.  In 
heavily  metalled  streets  the  rate  could  hardly  be  main- 
tained. 

There  is  no  doubt  whenever  possible  it  is  preferable 
to  lay  air  mains  beneath  the  footwalks.  Less  cover  is 
required,  and  they  are  free  from  the  dangers  of  steam 
rollers  and  heavy  traffic.  Also  a  lighter  type  of  surface 
box  for  valve  keys  is  required  than  if  placed  in  the 
street,  to  stand  heavy  wear  and  tear. 

In  laying  mains  of  this  description  through  populous 
streets  many  of  the  service  lead  water  pipes  to  the  houses 
will  be  broken  by  the  labourers'  picks.  The  same  may 
be  said  for  the  gas  pipes,  and  the  Company's  turncocks 
and  plumbers  should  always  be  present  to  prevent 
excessive  waste.  Such  pipes  are  easily  repaired,  but 
they  should  be  done  at  once  by  men  on  the  spot  to 
avoid  inconvenience. 

CAULKING  PIPE  JOINTS. 

To  make  an  efficient  joint  with  spigot  and  socket  pipes, 
the  following  materials  are  required  :  tarred  yarn,  stiff 
clay,  and  soft  pig  lead.  Scrap  lead  that  has  been  re- 
melted  many  times  is  hard  and  quite  unsuitable  for  air- 


124     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

main  joints.  In  using  such  lead  there  is  always  the 
danger  of  the  caulker  bursting  the  socket  of  the  pipe 
with  the  caulking  tool  in  making  the  joint  tight.  The 
pipe  socket  is  usually  four  inches  deep.  A  gasket  of 
tarred  yarn  is  rammed  home  round  the  spigot  end  of  the 
pipe  after  it  has  been  inserted  in  the  socket.  A  special 
band  or  short  length  of  one -inch  rope  is  smeared  with 
clay  and  placed  round  the  socket,  in  order  to  close  the 
open  end — the  plastic  clay  effectually  makes  a  '  tight 5 
joint — and  a  small  space  is  left  on  the  top  for  pouring 
in  the  lead.  The  lead  must  be  hot,  but  not  burnt.  If 
too  cold  it  will  fail  to  run  evenly  and  leave  a  spongy 
ring,  in  which  case  a  sound  joint  cannot  be  made.  Bad 
running  is  the  chief  cause  of  leaky  joints.  A  well-run 
joint  can  be  caulked  to  refusal.  With  good  workmen 
there  are  few  trimmings  ;  they  should  not  be  cut  off,  but 
permitted  to  *  fall  away '  as  the  caulking  tool  travels 
round  the  joint. 

TESTING  Am  MAINS  WHEN  LAID. 

Contractors  usually  favour  portable  steam  com- 
pressors for  testing  purposes.  Two  hundred  yards  is 
the  maximum  length  that  should  be  tested  at  one  time. 
The  longer  the  length  the  better  the  result  should  be, 
owing  to  the  expansive  nature  of  the  compressed  air. 
To  test  the  completed  length,  blank  flanges  are  clamped 
to  each  end  of  the  main  with  the  necessary  connections 
for  air  supply  and  pressure  gauge.  The  engine  is  started 
and  the  pressure  raised  to  the  stipulated  figure,  when  it 
is  stopped  and  the  fall  in  pressure  in  one  hour  noted. 

If  the  compressor  happens  to  be  in  the  next  street  and 
not  in  view  of  the  gauge,  it  is  as  well  to  see  that  it  is 
not  restarted  at  any  time  during  the  test.  If  the  jointing 
has  been  well  done,  it  will  be  found  that  with  an  initial 


FAULTS  AND  REMEDIES  125 

pressure  of  50  Ibs.  to  the  square  inch  the  loss  will  not 
exceed  1  Ib.  or  2  Ibs.  per  hour. 

DETECTING  LEAKAGE. 

The  application  of  soapsuds  to  all  joints  will  immedi- 
ately indicate  any  leakage.  It  is  by  no  means  uncommon 
to  find  that  if  leakage  exists  in  spite  of  all  the  joints 
being  sound,  a  pipe  has  been  cracked  in  transport  or  a 
socket  in  caulking.  Some  settlement  is  inevitable,  and 
it  is  a  wise  precaution  in  estimating  to  allow  a  sum  for 
recaulking.  After  twelve  months  or  so,  when  once  the 
pipes  have  become  firmly  bedded,  the  joints  alone  can 
be  opened  up  and  recaulked  with  little  fear  of  further 
leakage.  Care  should  be  taken  that  contractors  do 
not  lay  odd  lengths  of  pipe,  or  much  difficulty  will  be 
found  in  locating  the  joints  from  the  surface. 

The  smaller  sizes  of  cast-iron  pipes  give  more  trouble 
from  leakage  and  fracture  than  those  of  large  dimensions. 
The  joints  are  more  difficult  to  caulk,  and  the  pipes  will 
not  stand  any  strain  from  uneven  bedding. 

In  some  cities  where  the  subsoil  contains  many  old 
foundations,  even  a  bad  leak  running  away  with  100,000 
feet  of  air  per  day  will  never  come  to  the  surface  and 
is  only  located  by  sectional  testing.  With  a  properly 
organised  staff  this  is  not  a  long  operation.  A  leak 
of  such  magnitude  immediately  causes  the  driver  at 
the  power  house  to  increase  the  speed  of  his  engine  to 
maintain  the  air  pressure.  The  outside  staff  are  warned 
and  are  soon  able  to  locate  and  isolate  the  section.  In 
some  cases  essence  of  peppermint  may  be  put  into  the 
air  main  and  the  leakage  detected  by  smell,  but  with 
tarred  streets  and  asphalt  paving  this  is  not  very  success- 
ful. The  best  method  is  simply  to  locate  the  worst 
sections  between  stop  valves,  excavate  the  joints  from 


126    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

the  two  ends  and,  when  the  gauge  indicates  the  pres- 
sure is  again  normal,  fill  in  and  leave  the  remainder  of 
the  pipe. 

FILLING  TRENCHES  AND  RAMMERS. 

Subsequent  settlement  of  air  mains  depends  very 
much  on  the  method  of  filling  the  trench.  As  before 
stated,  the  pipes  should  be  laid  on  unbroken  ground — 
that  is,  on  trench  bottom — but  it  is  not  always  possible 
to  do  this.  The  ramming  of  the  earth  round  the  pipes 
is  of  extreme  importance  but  rarely  given  the  atten- 
tion it  merits. 

It  is  a  common  thing  to  use  ordinary  mushroom - 
headed  stone  rammers  of  8  ins.  or  9  ins.  in  diameter  ; 
but  they  are  not  suitable,  and  will  not  '  pack  the  earth  ' 
below  the  pipe.  Subsidence  and  leakage  are  the  result. 
The  rammers  for  this  class  of  work  should  be  of  the 
pattern  used  by  moulders  in  the  foundry,  with  small 
rectangular  heads,  and  weigh  6  Ibs .  or  7  Ibs .  By  using  such 
rammers  on  either  side  of  the  pipe  it  will  be  found  the 
earth  can  be  packed  against  the  underside  of  the  pipe 
as  efficiently  as  the  moulder  packs  the  sand  round  his 
patterns.  Soft  earth  only  should  be  placed  immedi- 
ately against  the  pipe.  Large  stones  and  dry  rubbish, 
which  the  soil  often  consists  of,  will  not  do. 

WATER  IN  AIR  MAINS. 

In  all  long  lengths  of  air  main  a  certain  amount  of 
condensation  takes  place.  Though  most  of  the  water 
will,  no  doubt,  pass  out  through  the  ejectors  as  they 
are  always  at  the  lowest  levels,  drain  cocks  should  be 
provided  in  all  sections  where  water  is  likely  to  collect. 
A  saddle -piece  should  be  clamped  on  to  the  pipe,  a  hole 
drilled  and  tapped  before  the  pipe  is  laid,  and  a  f -in.  pipe 


. 
FAULTS  AND  REMEDIES  127 

with  brass  plug  cock  brought  to  the  surface,  over  which 
is  placed  a  cast-iron  surface  box. 

AIR  STOP  VALVES. 

One  of  the  chief  causes  of  leakage  is  due  to  unsuitable 
stop  valves  on  the  air  mains.  To  prevent  leakage  these 
require  to  be  of  the  type  that  cannot  leak  past  the  spindle 
when  the  valve  is  open.  Packing  soon  perishes  under- 
ground, and  there  is  no  room  to  repack  glands  through 
a  key  box. 

The  ordinary  type  of  steam  valve  with  loose  valve 
and  packed  stuffing-box  is  not  suitable.  It  soon  leaks, 
and  grit  and  moisture  often  make  it  inoperative. 

Plate  XVI.  shows  a  type  of  valve  that  has  proved  very 
satisfactory  in  practice  on  underground  air  mains. 

It  is  simple  in  construction  and  easy  to  dismantle  for 
cleaning.  All  valves  that  have  to  remain  for  years 
underground  soon  become  corroded,  and  the  studs  fre- 
quently break  off  when  the  nuts  cannot  be  removed. 

In  this  valve  there  are  no  studs .  Four  bolts  fit  into  slots 
in  the  cap  and  bottom  cover.  The  principal  feature,  how- 
ever, is  the  security  from  leakage  when  the  valve  is  open. 

The  air-main  valves  remain  open  for  years  ;  in  the 
ordinary  type  the  packing  perishes  and  the  air  leaks 
past  the  spindle.  But  in  this  valve  a  collar  is  turned  on 
the  spindle  and  screwed  hard  down  on  to  a  copper  face 
when  the  valve  is  open.  The  nut  for  operating  the  valve 
is  removed  from  the  fluid,  and  the  single  central  guide 
with  the  valve  attached  does  not  become  fouled,  nor  is 
it  liable  to  jam  as  sometimes  happens  with  ordinary 
designs.  The  gland  and  stuffing-box  are  provided  for 
testing  purposes  so  that  the  pressure  can  be  applied  in 
either  direction,  and  the  valve  can  also  be  used  as  a 
regulator  if  so  desired. 


128     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

Referring  to  Plate  XVI.,  Fig.  1  is  a  plan,  Fig.  2  is  a 
section,  and  Fig.  3  an  elevation,  a,  is  the  valve  casing, 
b  the  inlet,  c  the  outlet,  d  the  plug  in  the  casing.  The 
valve  stem  e  is  provided  with  a  collar  /,  adapted  to  bear 
on  the  face  g  of  the  casing  a.  h  is  a  hollow  cap,  through 

PLATE  XVI 


UjJJ 
Section  Fig.2.  Elevation     Fig.  3. 

Am  STOP  VALVE 

which  the  stem  e  passes.  The  stem  e  is  screwed  at  i 
and  engages  with  a  nut .;'  disposed  in  the  cap  h.  The  cap 
k  and  plug  d  are  clamped  to  the  casing  a  by  bolts  jj 
which  pass  outside  of  the  casing,  k  is  the  copper  washer 
between  the  collar  /  and  the  face  g  of  the  casing,  ra  is 
a  hollow  valve  on  the  stem  e,  adapted  to  bear  on  the 


FAULTS  AND  REMEDIES  129 

valve  seat  n.    o  is  a  nut  for  securing  the  hollow  valve 
m  on  the  stem  e. 

VALVE  CHAMBERS. 

In  large  systems  the  expense  of  building  several 
hundred  masonry  valve  chambers  amounts  to  a  large 
figure,  and  may  well  be  omitted.  Even  the  best  of 
masonry  chambers  does  not  prevent  extensive  deteriora- 
tion, and  unless  they  are  large  and  deep  a  valve  cannot 
be  removed  without  breaking  the  brickwork. 

A  satisfactory  method  of  dispensing  with  the  brick 
chamber  is  as  follows. 

Having  well  greased  both  nuts  and  spindle,  and  tarred 
the  valves,  bury  the  valve  to  the  level  of  the  cap.  Place 
several  bricks  round  the  cap  and  rest  a  stoneware  pipe 
upon  them.  Fill  in  the  earth,  place  more  bricks  round 
top  of  the  pipe,  over  the  spindle,  and  on  these  rest  the 
cast-iron  surface  box  for  inserting  the  key.  Fill  in 
round  the  box  and  make  up  the  road,  and  there  will  be 
no  occasion  to  disturb  it  or  anything  more  than  the 
expense  of  excavation  if  it  is  desired  to  remove  the 
valve.  This  method  will  save  a  great  deal  of  expense 
in  construction  and  maintenance,  especially  if  the  type 
of  valve  shown  on  Plate  XVI.,  page  128,  is  utilised. 

ACCIDENT  TO  AIR  MAINS. 

Owing  to  the  low  pressure  there  is  no  fear  of  an  air 
main  bursting  in  the  ordinary  sense. 

Accidents  will  occur  now  and  again :  a  steam  roller  will 
fracture  a  pipe  if  the  ground  subsides  in  remaking  the 
street,  and  air  mains  break  from  the  tubbings  after  heavy 
rains.  Such  mishaps  are  easily  detected.  Again,  gas 
companies'  mechanics  sometimes  mistake  the  air  mains 
for  gas  mains  when  they  are  making  new  connections 

I 


130     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

to  street  lamps  and  dwellings,  and  do  not  discover  the 
difference  till  the  hole  has  been  cut  in  the  pipe. 

If  mains  refuse  to  pass  the  volume  of  air  it  will  prob- 
ably be  found  that  a  valve  has  become  jammed  in  its 
seat,  the  nut  screwed  off,  and  the  turn-key  instead  of 
opening  the  valve  withdraws  the  spindle  from  the  hole. 

LAYING  RISING  MAINS. 

In  the  laying  of  sealed-sewage  mains  the  precautions 
adopted  with  water  mains  should  be  observed,  but  at 
all  bends  an  inspection  opening  should  be  provided  and 
extreme  care  taken  that  a  '  badger  '  is  drawn  through 
the  pipes  before  they  are  closed.  If  this  is  not  done 
articles  are  liable  to  be  left  in  the  pipes  during  the  process 
of  construction.  Whole  bricks  from  6-in.  mains  have  been 
removed,  and  timber  struts  3  ft.  long  and  4  ins.  square, 
sacking,  balls  of  caulking  yarn,  and  suchlike  articles. 
Again,  lead  passing  through  the  joint  into  the  invert  of 
the  pipe  is  sufficient  to  form  an  obstruction  after  some 
months'  work.  When  the  pipes  are  first  put  into  use 
the  effluent  passes,  but  after  a  time  the  accumulation 
of  solids  completely  chokes  the  main,  and  there  is  nothing 
for  it  but  to  cut  out  the  pipes  and  relay  them. 

BACK  PRESSURE  IN  MAINS. 

In  cases  where  more  than  one  ejector  discharges  into 
the  same  main  by  long  lengths  of  branch  pipe,  care 
must  be  taken  that  these  small  mains  are  not  choked  by 
back  pressure,  or  many  yards  of  pipe  will  become  filled 
with  solid  matter  which  can  only  be  removed  by  cutting 
out.  The  remedy  for  the  trouble  is  obvious. 

It  is  surprising  what  large  articles  will  pass  through 
these  pipes  without  stoppage.  It  may  be  taken  for 
granted  that  any  substance  that  will  pass  through  the 


FAULTS  AND  REMEDIES  131 

ejector  will  pass  up  the  rising  main,  provided  there  is 
sufficient  water  and  no  constructional  fault. 

FOULING  OF  MAINS. 

During  the  first  two  or  three  years  a  certain  amount 
of  fouling  of  the  mains  will  take  place,  and  more  pres- 
sure will  be  required  to  discharge  the  ejectors.  After 
the  pipes  are  coated  inside  to  a  certain  extent  it  does 
not  appear  to  be  progressive. 

LOCATING  STOPPAGE  IN  MAINS. 

With  a  choked  main  the  reflux  valve  is  first  opened, 
to  see  if  all  is  clear.  Then  the  first  inspection  chamber 
is  excavated,  and  a  pressure  gauge  fixed  in  the  cover.  If 
there  is  no  pressure  the  stoppage  is  down  stream.  The 
main  is  excavated  half-way  between  the  chamber  and 
reflux  valve,  a  hole  drilled,  and  pressure  gauge  fixed.  If 
there  is  still  no  pressure  another  hole  is  drilled,  and  so 
on  till  the  block  is  located. 

AIR  LOCK  IN  MAINS. 

In  cases  where  a  rising  main  is  laid  at  a  steep  grade 
and  suddenly  falls,  it  is  necessary  to  provide  an  air-cock 
just  beyond  the  highest  point,  if  not  a  permanent  atmo- 
spheric pipe,  or  trouble  will  arise  from  air  lock  and  diffi- 
culty will  be  experienced  in  making  the  ejector  discharge 
under  normal  pressure. 

INSPECTION  OPENINGS  AND  BENDS. 

As  a  rule  inspection  openings  are  provided  in  sealed- 
sewage  mains  at  all  bends,  and  every  100  yds.  in  pipes 
less  than  10  ins.  in  diameter,  though  90  per  cent,  of 
them  will  ceitainly  never  be  required.  The  covers  should 
be  drilled  and  tapped  for  a  pressure  gauge,  as  when  the 


132     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

main  becomes  choked  they  may  save  the  cover  being 
removed  by  indicating  if  the  block  is  up  or  down  stream. 
Again,  all  bends  should  be  backed  by  timber  struts 
firmly  driven  into  the  ground,  or  by  a  block  of  concrete, 
as  the  pressure  is  liable  to  force  the  joint  and  cause 
leakage.  Care  must  be  taken  that  the  concrete  does  not 
rest  on  the  pipe,  or  settlement  of  the  masonry  will  start 
the  joint  and  cause  leakage. 

SCOUR  VALVES. 

In  all  long  lengths  of  main  there  should  be  a  scour 
valve  that  can  discharge  into  the  gravitation  sewers, 
as  it  is  not  only  advisable  to  discharge  any  solid  matter 
from  time  to  time  that  may  collect  in  the  depressions, 
but  if  the  sewage  main  has  to  be  opened  it  is  an  extremely 
unpleasant  business,  flooding  the  street  with  crude 
sewage.  At  all  junctions  sluice  valves  are  required,  and 
these  must  be  operated  periodically  or  they  will  become 
absolutely  fast.  All  valves  should  be  right-handed  and 
of  the  same  pattern,  and  covered  over  with  a  surface 
box  as  already  described,  for  air  stop  valves. 

BURSTING  OF  MAINS. 

This  is unknownf rom  internal  pressure .  Joints  have  been 
known  to  give  out  and  inspection  chambers  crack,  but  if 
laid  with  3-ft.  cover  there  is  practically  no  danger  unless 
a  steam  roller  or  such  heavy  vehicle  cause  subsidence. 

INDICATOR  PLATES. 

Sluice  valves,  air  valves,  and  inspection  openings 
should  all  have  their  positions  indicated  by  an  iron  plate 
fixed  in  the  nearest  wall,  showing  the  distance  at  which 
it  is  located,  much  in  the  same  way  as  the  fireman's 
water  cocks. 


CHAPTER  VIII 
THE  SANITARY  EFFICIENCY 

THE  sanitary  efficiency,  though  left  till  last,  is  by  no 
means  the  least  important.  Properly  speaking,  it  should 
be  dealt  with  by  experts  in  public  health,  as  it  is  some- 
what outside  the  province  of  the  engineer  to  say  what  is 
a  public  nuisance  and  what  is  not,  or  what  is  dangerous 
to  health,  and  what  is,  and  what  is  not  an  offensive 
odour.  In  fact,  the  precise  definition  of  '  efficient  sani- 
tation '  in  the  matter  of  the  collection  and  conveyance 
of  domestic  sewage  is,  and  will  remain,  a  matter  of 
opinion  ;  but  the  last  word  invariably  rests  with  the 
public  health  authorities,  and  it  is  the  engineer's  function 
to  provide  the  means  to  conform  with  the  stipulations 
laid  down. 

On  his  skill  and  experience  will  depend  the  provision 
of  the  most  efficient  means  of  carrying  out  the  work 
to  be  done  with  the  funds  available. 

The  ideal,  though  unattainable,  must  be  steadily  kept 
in  view.  Make  certain  of  the  essentials  either  large  and 
small,  and  economies  will  suggest  themselves  as  the 
scheme  is  designed. 

GRAVITATION  SCHEME. 

Though  the  simple  gravitation  scheme  has  been  ex- 
cluded from  these  pages,  it  is  obviously  adopted  without 
question  whenever  the  necessary  levels  permit ;  but  it 
must  not  be  taken  for  granted  that  such  a  scheme  always 

183 


134     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

possesses  sanitary  efficiency,  or  in  exceptional  cases  is 
the  cheapest  to  construct  and  maintain.  For  instance, 
in  situations  where  a  gravitation  scheme  necessitates 
sewers  of  great  depth  in  water-logged  soil,  and  little  fall 
can  be  provided,  the  expense  of  excavation  and  de-water- 
ing, together  with  cleaning  choked  sewers,  difficulty  of 
flushing,  and  repairs,  will  amount  to  a  higher  capital  cost 
and  maintenance  than  a  system  of  shallow  sewers  with 
efficient  and  reliable  means  for  conveying  the  effluent  to 
the  disposal  works. 

Or  again,  it  is  not  unusual  to  find  localities  in  which 
some  sections  are  able  to  be  drained  by  gravitation,  while 
others  require  some  means  of  raising  the  sewage  into  a 
high-level  sewer. 

There  is  no  object  in  wasting  power  to  raise  sewage 
when  it  will  flow  by  gravitation  to  the  desired  outfall, 
even  when  by  so  doing  some  expense  can  be  saved  in 
the  original  construction. 

A  single -main  outfall  with  a  single -disposal  works  can 
be  allowed  for  with  the  exception  of  those  cities  that 
discharge  their  sewage  direct  into  the  sea.  Whether 
this  method,  however,  can  be  described  as  coming  within 
the  definition  of  'sanitary  efficiency'  is  a  subject  that 
will  not  be  discussed  here. 

No  two  undertakings  are  precisely  alike.  Each  case 
must  be  considered  independently  on  its  merits.  A 
satisfactory  system  for  an  urban  district  in  Europe  may 
be  a  danger  to  health  in  semi-tropical  countries. 

THE  SUBSOIL. 

The  nature  of  the  subsoil  in  the  area  to  be  drained 
should  be  carefully  studied.  The  sanitary  efficiency 
will  depend  to  a  great  extent  on  reliable  information 
from  this  source. 


THE  SANITARY  EFFICIENCY  135 

However,  few  authorities  care  to  go  to  the  expense  of 
mapping  out  a  whole  district  before  commencing  opera- 
tions, as  unless  a  very  regular  geological  formation  exists, 
it  would  entail  the  sinking  of  many  trial  shafts  and  bore- 
holes. Nevertheless  in  some  localities  it  is  a  question  if 
the  extra  expense  would  not  be  more  than  covered  by  the 
definite  information  on  which  estimates  could  be  drawn  up, 
and  the  saving  in  sound  construction  in  the  first  instance. 

In  a  sectional  scheme  of  great  extent  there  is  little 
doubt  that  an  excavation  on  the  site  of  the  proposed 
ejector  stations  is  well  worth  the  trouble.  Instances 
have  been  known  where  sites  have  been  selected  and 
operations  carried  so  far,  that  it  has  been  cheaper  to  sink 
a  tubbing  through  solid  rock  than  to  alter  the  whole 
sewering  scheme  of  an  area.  To  excavate  rock  in  a 
compressed-air  chamber  by  candlelight  is  an  extremely 
costly  and  tedious  business,  and  the  only  alternative 
is  to  go  to  the  heavy  expense  of  keeping  a  steam  pump 
constantly  at  work  with  the  difficulty  of  disposing  of  the 
water  in  crowded  streets. 

The  advantage  of  possessing  complete  information  of 
the  subsoil  will  be  understood  from  a  glance  at  the  plan 
and  ground  sections  shown  in  the  following  diagrams. 
Plate  XVII.  shows  a  plan  of  the  city  of  Cairo  on  which 
is  marked  the  sites  of  sixty-three  ejector  stations. 
The  numbers  prefixed  by  a  capital  letter  refer  to  deep 
boreholes  and  excavations  made  in  the  construction  of  the 
bridges  that  span  the  Nile .  Plates  XVIII.  and  XIX .  show 
sections  through  the  soil,  the  vertical  line  indicating  the 
position  of  an  excavation.  These  diagrams,  however, 
were  made  from  the  information  derived  in  sinking  the 
cast-iron  tubbings  and  not  from  previous  excavations, 
but  their  value  was  obvious  in  the  construction  of  the 
deeper  sewers. 


136     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

The  various  strata  of  the  Nile  valley  may  not  be  pre- 
cisely reproduced  elsewhere,  but  river  deltas  have  many 
points  in  common,  and  the  cities  standing  thereon  are 
subject  to  many  of  the  same  conditions. 

PLATE  XVII 


PLAN  OF   CAIRO 
UNDERGROUND   STRUCTURE 


On  looking  at  the  plan  of  the  city,  Plate  XVII.,  the  area 
of  the  impervious  clay  deposit  will  be  noticed.  It  is 
that  portion  within  the  hatched  outline .  The  sites  appear 
to  be  selected  in  a  haphazard  manner,  but  it  must  be 


THE  SANITARY  EFFICIENCY  137 

remembered  that  they  are  situated  for  the  most  part  on 
the  flats ,  and  in  the  depressions  which  formed  con- 
venient localities  to  which  the  sewers  would  gravitate. 
This  will  also  explain  the  inequality  of  the  sections  taken 
and  the  reason  why  the  imaginary  lines  do  not  precisely 
bisect  each  site.  However,  they  are  so  numerous  that 
this  inaccuracy  can  hardly  affect  the  general  outline  as 
depicted.  In  such  diagrams  extending  for  miles,  it  is 
obvious  that  the  vertical  scale  must  be  larger  than 
the  horizontal  scale  in  order  to  bring  into  prominence 
the  correct  levels,  and  their  relative  proportions  should 
not  be  overlooked.  The  area  covered  is  approximately 
6x3  miles .  On  the  west  is  the  Nile  and  to  the  east  the 
stony  desert. 

The  index  letters  on  the  sections  correspond  with  those 
upon  the  plan,  and  the  excavations  have  been  numbered 
in  such  a  manner  that  any  particular  site  can  be  located 
at  a  glance  in  spite  of  their  irregular  position.  The  general 
characteristics  of  the  soil  are  well  illustrated  in  Plate  VIII., 
page  26,  and  may  be  summed  up  briefly  as  follows. 
Commencing  with  the  surface  we  have  in  most  cases  a 
deep  layer  of  builders'  rubbish.  The  remains  of  house 
after  house  have  decayed,  fallen,  and  been  trodden  under 
foot  till  the  original  ground  levels  have  been  entirely 
obliterated  and  artificial  hills  have  appeared.  Virgin 
loam  is  seldom  met  with  except  in  outlying  portions  of 
the  city.  Secondly,  a  natural  deposit  of  stiff  plastic  clay 
which  varies  in  thickness  from  3  feet  to  12  feet.  Thirdly, 
a  vast  mass  of  interbedded  fluid  sands,  the  upper  layers 
of  which  are  frequently  as  fine  as  ground  pepper,  and 
coarser  varieties  beneath  from  which  an  inexhaustible 
supply  of  water  can  be  drawn. 

The  most  remarkable  feature  of  these  deposits  is  without 
doubt  the  basin  or  depression  in  the  clay  bed,  which  can 


& 


THE  SANITARY  EFFICIENCY  139 

be  clearly  seen  in  section  E.F.  (Plate  XVIII.).  At  least 
this  is  how  it  appears  in  the  diagram,  but  it  is  in  reality 
an  extensive  lake  or  lagoon  which  underlies  the  centre 
of  the  city. 

On  sections  M.N.  (Plate  XVIII.)  and  H.J.  (Plate  XIX.) 
the  high  and  low  level  of  the  Nile  will  be  noted.  Obviously 
when  the  annual  inundation  rises  above  a  certain  level, 
the  lake  is  replenished,  while  throughout  the  year  (before 
the  drainage  scheme  existed)  it  is  incessantly  fed  by  the 
drainage  from  the  houses.  And  this  water  must  either 
be  absorbed  by  the  accumulated  rubbish,  or  flow  over 
the  edge  of  the  basin  into  the  Nile  through  the  porous  soil. 

Section  M.N.  is  of  particular  interest,  as  the  first  and 
last  excavations  on  the  surface  show  what  is  practically 
true  ground  level,  and  the  lowest  level  is  that  furthest 
from  the  river  bank.  A  certain  amount  of  water  always 
overlays  the  clay  bed,  and  is  often  only  a  few  feet  from 
the  surface,  but  if  the  clay  bed  is  pierced  not  only  water 
but  sand  will  continue  to  rise  as  fast  as  it  is  removed.  For 
this  reason  excavation  in  such  soil  is  very  costly  without 
the  use  of  compressed  air. 

From  the  sanitary  point  of  view,  the  advantage  of 
shallow  sewers  is  also  obvious  under  such  conditions,  as 
stoneware  pipes  that  are  laid  in  a  porous  soil  which  is 
alternately  saturated  and  drained  each  year  are  liable 
to  some  settlement  which  cracks  the  joints.  The  result 
is  the  subsoil  water  leaks  into  the  pipes  when  they  are 
submerged,  and  the  sewage  leaks  out  when  the  subsoil 
water  subsides.  It  is  almost  unnecessary  to  state,  if  the 
sewage  leaks  out  of  the  sewer  in  any  quantity  in  porous 
soil,  the  state  of  the  ground  is  little  better  than  if  perco- 
lating cess-pits  existed.  It  must  however  be  pointed  out 
that  because  a  large  volume  leaks  in,  it  is  no  proof  that 
an  equally  large  volume  leaks  out.  In  fact,  there  is  no 


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THE  SANITARY  EFFICIENCY  141 

question  that  it  does  not,  provided  the  ejectors  are  kept 
working  and  no  '  head  '  is  placed  on  the  sewers.  When 
stoneware  sewers  are  placed  under  an  external  pressure 
of  10-ft.  head  of  water,  it  is  clear  that  the  whole  circum- 
ference of  a  cracked  joint  will  admit  water  ;  on  the  other 
hand,  a  sewer  in  the  same  condition  in  dry  soil,  running  a 
third  full,  will  show  insignificant  leakage  in  comparison. 

CONDITIONS  FOR  SANITARY  EFFICIENCY. 

Atmospheric  conditions  must  be  studied,  prevailing 
winds  carefully  noted,  nature  of  the  soil,  source  and 
method  of  water  supply,  and  particular  attention  given 
to  providing  such  arrangements  as  will  facilitate  future 
extensions.  Again,  if  the  district  is  subject  to  a  heavy 
rainfall,  it  may  be  advisable  to  adopt  a  separate  system 
for  surface  water,  as  distinct  from  house  sewerage, 
especially  if  the  effluent  has  to  be  raised  to  the  disposal 
works  under  a  high  pressure.  If  a  single  system  was 
adopted  in  such  cases,  the  cost  per  head  of  the  popula- 
tion would  amount  to  an  unreasonable  figure.  In  the 
majority  of  cases,  rain  water  may  be  discharged  into  a 
tidal  way  or  river  without  offence — that  is  to  say,  what 
is  usually  termed  '  flood  water ' — but  provision  has  to  be 
made  for  street  sweepings  to  run  into  the  house  sewerage 
system. 

The  initial  expense  of  laying  separate  sewers  for  each 
purpose  is  heavy,  and  a  series  of  overflows  is  the  most 
favoured  arrangement.  With  the  progress  of  sanitary 
engineering  the  question  of  sanitary  efficiency  comes  to 
be  more  and  more  considered,  and  the  more  densely  a 
district  is  populated  the  more  difficult  it  is  to  find  sites 
for  purification  works  and  pumping  stations.  No  scheme 
that  does  not  provide  for  purifying  the  effluent  can  be 
entertained  at  the  present  day.  It  is  an  essential  part 


142     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

of  the  whole,  and  second  only  in  importance  to  the 
rapid  conveyance  of  the  raw  sewage  from  house  sewers 
beyond  the  precincts  of  habitations. 

If  the  grade  to  which  the  sewers  are  laid  is  not  suffi- 
ciently steep,  putrefaction  of  the  effluent  will  take  place 
and  noxious  odours  will  be  disseminated  ;  but  in  the 
absence  of  natural  fall,  deep  sewers  must  be  laid  to  avoid 
this  unless  the  sectional  system  is  adopted. 

SECTIONAL  SYSTEM. 

Briefly,  the  sectional  system  of  sewering  a  town  or 
district  is  simply  dividing  the  district  up  into  a  number 
of  suitable  sections.  The  lowest  site  in  each  section  is 
chosen  for  a  sump  or  collecting  manhole,  and  all  street 
sewers  in  the  section  converge  to  this  spot.  Either  a 
pump  or  an  ejector  is  located  at  this  spot  and  the  sewage 
is  pumped  into  a  sealed  cast-iron  main,  which  discharges 
the  liquid  at  the  disposal  works,  or  into  a  high-level 
gravitation  sewer,  if  the  site  of  the  disposal  works  and 
levels  of  the  surrounding  country  permit.  Let  us  analyse 
the  differences  between  the  pump  and  the  ejector  for 
such  a  purpose  and  see  why  one  has  a  better  sanitary 
efficiency  than  the  other. 

The  outstanding  difference  is  that  a  pump  requires 
a  cess-pit  or  sump  to  draw  from,  and  a  screening  chamber 
to  collect  refuse  which  has  to  be  periodically  removed 
and  handled.  The  level  of  the  liquid  in  such  a  sump 
varies,  and  large  surfaces  to  which  the  floating  matter 
in  the  effluent  clings  are  exposed  to  putrefaction.  The 
cleaning  of  this  sump  and  screening  chamber  is  not  only 
repulsive  but  a  dangerous  occupation,  as  lights  are  in- 
variably needed  to  work  by  and  explosions  are  liable  to 
take  place  from  foul  gases  with  disastrous  results.  With 
the  ejector  as  previously  described,  there  is  no  sump. 


THE  SANITARY  EFFICIENCY  143 

The  sewer  discharges  into  the  body  of  the  ejector,  which 
automatically  forces  the  effluent,  together  with  all  refuse, 
into  the  rising  main  at  frequent  intervals. 

GRADE  OF  SEWERS. 

To  ensure  sanitary  efficiency,  especially  in  tropical 
and  semi-tropical  climates,  this  is  a  necessity,  and  the 
sewers  must  be  laid  at  such  a  grade  that  the  effluent 
arrives  at  the  ejector  before  putrefaction  sets  in.  Grades 
of  130  to  150  in  street  sewers  are  not  unusual,  and  this 
gives  a  velocity  that  permits  of  this  desirable  end  being 
attained. 

It  will  be  observed  that  the  ejector  inlet  shown  on 
Plate  VIII.,  page  26,  is  placed  at  such  a  level  that  the 
sewers  are  kept  drained.  No  collection  or  putrefaction 
can  take  place  in  the  sewer,  therefore  no  foul  gases  are 
formed.  Fresh  sewage  is  inoffensive.  The  mechanical 
apparatus  that  will  deal  with  the  sewage  as  fast  as  it 
comes  down  the  sewers,  has  a  higher  sanitary  efficiency 
than  an  apparatus  which  permits  collection  and  decom- 
position, and  the  ejector  is  far  superior  in  this  respect. 
In  durability  and  freedom  from  breakdown  it  has  no 
equal  and  supervision  is  reduced  to  a  minimum. 

The  pneumatic  ejector  is  to  be  preferred  to  a  pump, 
whenever  the  locality  is  of  such  a  nature  that  the  capital 
expenditure  and  cost  of  maintenance  is  not  out  of  all 
proportion  to  the  results  obtained.  Even  in  small  in- 
stallations the  points  are  in  favour  of  the  ejector. 

REASONS  OF  PREFERENCE  FOR  SMALL  PUMPS. 

That  small  centrifugal  pumps  are  so  often  installed 
in  country  towns  and  large  villages  is  almost  invariably 
due  to  the  high  efficiency  on  trial  results  that  the  maker 
is  able  to  put  before  the  consulting  engineer,  and  the 


144     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

reduced  initial  outlay  on  machinery,  without  regard  to 
the  efficiency  of  the  pumps,  in  a  few  years'  time,  or  the 
cost  of  deep  sewers.  Again,  great  weight  is  often  attached 
to  the  fact  that  the  ejectors  would  have  to  be  kept 
continually  at  work  to  prevent  the  sewage  backing  up 
in  the  sewers,  whereas  with  a  pump  two  shifts  are  avoided, 
the  sump  being  of  such  a  capacity  that  it  can  be  per- 
mitted to  fill  up  during  the  night  after  having  been 
pumped  out  in  the  daytime.  But  the  flow  of  sewage  in 
such  places  during  the  night  is  but  a  small  percentage 
of  the  daily  flow,  and  there  is  no  reason  why  the  sewer 
should  not  be  enlarged  at  the  discharge  end,  with  a  water 
seal  upstream  to  avoid  any  unpleasant  effects  of  sewage 
accumulation.  It  would  be  flushed  and  drained  auto- 
matically in  any  case,  thus  obviating  the  periodical 
removal  of  refuse  and  cleaning  of  the  sump  which  takes 
place  with  pumping  installations. 
Let  us  take  an  example. 

TYPICAL  EXAMPLE  OF  SMALL  SEWERAGE  SCHEME. 

A  large  village  consisting  of  groups  of  houses  in  low- 
lying  ground,  and  others  on  high  ground,  is  advised  by 
the  local  authority  that  a  drainage  scheme  must  be 
carried  out  and  maintained  by  the  rates.  The  Local 
Government  Board,  or  whoever's  duty  it  is,  appoints  an 
engineer  to  survey  the  place  with  a  view  to  laying  down 
sewers  and  finding  a  suitable  place  for  disposal  works. 

He  soon  discovers  that  the  greater  part  of  the  sewage 
will  have  to  be  raised  by  some  means  or  other  to  the 
purification  works,  and  no  means  must  be  spared  in  his 
estimates  to  keep  the  cost  down  per  head  of  the  popu- 
lation to  a  reasonable  figure,  if  he  is  not  to  put  forward 
an  extravagant  scheme  which  will  be  rejected  and  injure 
his  career. 


THE  SANITARY  EFFICIENCY  145 

In  all  probability  he  is  without  experience  in  running 
pumps  or  ejectors,  and  has  little  knowledge  of  mechanics. 
Therefore  the  machinery  is  the  direction  in  which  to 
economise. 

What  does  he  do  ? 

He  has  two  alternatives  before  him.  Assuming  the 
total  head  with  friction  is  about  45  ft.,  he  has  choice  of 
installing  small  pumps  with  steam,  oil,  or  suction  gas 
engines,  excavating  and  building  a  deep  screening  cham- 
ber and  sump  and  laying  a  low-level  sewer  thereto, 
or  providing  two  or  three  small  ejector  stations  with  an 
oil-engine  air  compressor. 

The  disposal  works  are  common  to  both  schemes,  but 
need  not  be  of  such  magnitude  for  the  ejectors  as  less 
surface  water  would  be  dealt  with.  His  pumping  station 
and  sump  must  be  far  removed  from  habitations,  and 
difficulty  may  be  experienced  in  finding  a  site  that  does 
not  entail  the  laying  of  a  long  length  of  sewer  in  water- 
logged ground. 

On  the  other  hand,  his  ejector  stations  can  be  placed 
beneath  the  roads  in  just  those  spots  where  there  is  a 
local  depression  to  which  shallow  sewers  may  converge. 
His  air-compressor  station,  being  quite  inoffensive,  can  be 
placed  in  twenty  different  situations,  and  the  rising  main 
to  the  disposal  works  will  not  be  more  than  2  ft.  or  3  ft. 
below  the  surface. 

The  laying  and  cost  of  a  cast-iron  main  may  be 
calculated  to  definite  figures,  but  deep  sewers  often 
run  into  large  sums,  from  the  extra  cost  of  de- 
watering  and  heavy  timbering  to  prevent  subsidence. 
He  collects  what  information  there  is  on  the  cost  of 
machinery  and  studies  the  published  results  of  official 
efficiency  trials. 

According  to  these  the  ejectors,  besides  costing  more 

K 


146    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

to  install,  have  an  efficiency  of  only  38  per  cent,  com- 
pared to  72  per  cent,  of  a  pump. 

Obviously,  on  paper,  this  represents  a  large  saving  in 
maintenance.  What  more  convincing  evidence  can  an 
engineer  require  to  put  before  his  superiors  or  the  parish 
council  ? 

There  is  no  evidence  or  information  of  a  conclusive 
character  to  disprove  his  figures.  Five  or  ten  years 
hence  is  none  of  his  affair.  He  is  only  there  to  estimate 
the  cost,  and  supervise  the  carrying  out  of  the  work, 
which  will,  in  due  course,  be  handed  over  to  the  parish 
council.  Whatever  the  cost  of  running  may  be  will  be 
accepted  as  inevitable,  and  the  mechanic  employed  to 
supervise  the  machinery  will  neither  have  the  know- 
ledge nor  interest  to  compile  detailed  records  from  which 
posterity  may  benefit. 

The  question  of  city  drainage  becomes  more  and  more 
of  an  engineering  science. 

The  purification  of  the  effluent  has  reached  a  high 
state  of  perfection.  The  grading  of  sewers  for  suitable 
velocities  and  their  precise  capacities  has  been  reduced 
to  exact  formulas  ;  but  the  behaviour  of  power  engines 
and  the  apparatus  to  raise  the  sewage  is  too  often 
a  closed  book  to  those  in  authority  who  are  respon- 
sible for  the  construction  and  maintenance  of  sewage 
schemes. 


CHAPTER  IX 
POWER    HOUSE 

POWER  HOUSE 

THESE  notes  and  records  on  the  efficiency  and  cost  of 
raising  crude  sewage  by  pumps  and  pneumatic  ejectors 
would  be  incomplete  without  some  reference  to  the 
power  house.  Important  though  it  is  to  maintain  the 
ejectors  in  an  efficient  state,  we  can  do  nothing  without 
the  means  from  which  the  power  is  derived.  The  power 
house  is  the  centre  of  the  system  from  which  flows  the 
required  energy  in  every  direction. 

POWER  ENGINES  COMPARED. 

Whether  the  installation  consists  of  steam  engines, 
oil  engines,  or  gas  engines,  the  heat  is  the  power  and  the 
sewage  to  be  raised  is  the  work  to  be  done. 

With  the  steam  engine  the  heat  is  derived  from  the 
combustion  of  fuel  beneath  the  boiler  which  generates 
the  steam  for  actuating  the  engine,  which  converts  the 
fluid  energy  into  mechanical  power  for  compressing  the 
air  (which  is  a  secondary  power)  as  a  medium  of  trans- 
mission for  working  the  ejectors. 

With  the  oil  engine  the  combustion  of  the  fuel  takes 
place  in  the  cylinder  of  the  engine.  In  actual  fuel  con- 
sumption for  the  volume  of  air  compressed  there  is  a 
great  economy,  but  that  is  subject  to  a  uniform  output 
at  a  steady  pressure.  With  the  gas  engine  combustion 

147 


148     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

also  takes  place  in  the  cylinder  of  the  engine,  but  a  separate 
plant  has  to  be  provided  for  the  generation  of  the  gas. 

For  supplying  power  to  an  ejector  system  the  first 
requirements  are  reliability,  flexibility.  By  reliability  is 
meant  freedom  from  breakdown,  from  any  cause  whatever ; 
by  flexibility,  a  great  range  of  speed  and  power,  so 
that  a  constant  pressure  can  be  maintained  in  spite  of 
variation  in  speed. 

A  good  internal-combustion  engine  will  consume  0*50 
Ib.  of  oil  per  brake  horse -power  per  hour.  A  good 
superheated  steam  engine  will  consume  1*19  Ibs.  approx. 
of  coal  per  brake  horse -power  per  hour,  or  with  fuel  oil 
0*72  Ib.  per  brake  horse -power  per  hour. 

Given  a  sound  and  efficient  steam  unit,  it  will  prob- 
ably be  found  that  the  commercial  efficiency  of  the 
steam  plant  is  not  inferior  to  that  of  the  internal-com- 
bustion engine.  Indeed,  experience  shows  that  the  re- 
verse is  usually  the  case.  The  variation  in  the  demand 
for  power  over  the  twenty-four  hours  is  very  great, 
and  during  the  twelve  months  greater  still.  One  of  the 
most  difficult  questions  to  decide  in  specifying  the 
machinery  for  a  power  house  is  the  number  of  separate 
units  which  should  be  installed  to  make  up  the  maximum 
power  required. 

The  unit  that  will  give  the  highest  efficiency  over  the 
greatest  range  of  speed  is  the  most  efficient  for  running 
an  ejector  system.  The  larger  the  unit  the  higher  the 
efficiency  should  be,  but  there  is  a  limit  at  which  a  large 
unit  will  run  economically  at  low  speeds. 

When  internal-combustion  engine  compressors  are 
installed,  it  is  not  unusual  to  provide  a  by-pass  to 
atmosphere  from  the  compressor,  as  the  speed  of  the 
engine  cannot  be  reduced  sufficiently  when  the  consump- 
tion of  air  falls  to  a  low  figure.  But  this  is,  of  course, 


POWER  HOUSE  149 

extremely  wasteful,  and  the  economy  gained  in  one 
direction  is  thrown  away  by  extravagance  in  another. 

Much  depends  on  the  price  of  the  fuel. 

The  cheapest  quality  of  fuel  can  be  burned  under  a 
boiler,  but  a  more  expensive  grade  is  required  for  the 
internal-combustion  engine.  When  electric  current  can 
be  supplied  at  a  very  cheap  rate  from  water  power  or 
some  great  industrial  power  station,  a  variable -speed 
motor  compressor  should  be  considered.  The  capital 
cost  in  buildings  and  maintenance  should  be  much  less, 
but  some  form  of  sensitive  air  governor  would  be  required 
to  maintain  a  steady  pressure  under  varying  demands. 
To  run  an  engine,  no  matter  of  what  type,  against  a 
steady  pressure  makes  all  the  difference  between  waste 
and  economy,  and  herein  lies  one  of  the  chief  causes  of 
the  inefficiency  of  an  ejector  power  station ;  but  there 
is  little  doubt  this  drawback  is  open  to  improvement, 
and  will  be  dealt  with  in  the  next  chapter. 

There  is  no  intention  of  comparing  the  merits  or  dis- 
advantages of  the  various  designs  of  engines  and  com- 
pressors, but  it  may  be  remarked  that  it  pays  to  have 
machinery  of  the  highest  class. 

Plates  XIV.  and  XV.  (pages  70,  71)  show  the  interior 
of  the  large  compressor  station  for  operating  the  Cairo 
drainage  system.  They  are  triple -expansion  condensing 
engines,  with  double-acting  compressors,  direct  coupled 
to  tail  rods  from  the  three  steam  cylinders,  and  each 
compressor  is  provided  with  mechanically  operated  valves 
for  the  admission  and  discharge  of  the  air.  While  some 
engineers  favour  this  type  owing  to  their  flexibility, 
others  prefer  the  high-speed  vertical  type.  Such  engines 
take  up  less  room,  and  can  be  usually  guaranteed  to 
give  a  higher  efficiency.  Complicated  valve  gear  of  all 
descriptions  should  be  avoided ;  each  unit  should  be 


150     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

complete  in  itself,  and  arrangements  made  so  that  the 
engines  can  be  easily  started  under  pressure. 

POWER-HOUSE  DESIGN. 

The  power  house  should  be  designed  to  suit  the 
machinery.  That  is  to  say,  the  foundations  of  the 
engines,  their  spacing,  basement  requirements  for  pipes 
and  condensers,  boilers  and  their  accessories,  must  all 
be  carefully  drafted  out  in  a  general  arrangement — plans, 
elevations,  and  sections  complete,  showing  every  essential, 
such  as  dimension  of  engines,  position  of  chimney  stack, 
economiser,  cooling  pond,  and  the  various  levels  at 
which  it  is  proposed  water  shall  be  drawn  by  the  circu- 
lating pumps  for  the  condensers  and  compressor  jackets, 
also  the  method  of  replenishing  the  water  supply  and 
arrangements  for  carrying  it  away.  When  these  points 
have  been  carefully  decided  and  the  machinery  selected, 
it  is  simply  a  matter  of  providing  a  suitable  building  to 
cover  the  plant. 

There  is  nothing  more  expensive  or  unsatisfactory 
than  fitting  machinery  into  unsuitable  buildings  that 
have  already  been  designed.  A  municipal  power  house 
is  neither  an  orphanage  nor  a  factory,  and  there  is  no 
reason  why  the  architect  should  not  produce  as  handsome 
a  building  as  the  funds  at  his  disposal  permit.  The  walls 
must  be  built  to  carry  a  travelling  crane,  and  the  door- 
ways made  of  sufficient  dimensions,  or  other  facilities  pro- 
vided for  admitting  the  largest  sections  of  the  machinery 
into  the  building.  There  is  nothing  more  exasperating 
than  having  to  knock  holes  in  a  new  wall  or  cut  out 
windows  before  the  engine  can  be  put  together. 

FOUNDATIONS  FOR  MACHINERY. 

The  extent  and  massiveness  of  the  foundations  depends 


POWER  HOUSE  151 

a  great  deal  on  the  nature  of  the  soil  and  type  of  engine. 
The  foundations  must  be  quite  separate  from  the  walls 
and  floors,  and  the  chimney  shaft  well  clear  of  the  build- 
ing. If  the  subsoil  is  water-logged  sand,  as  is  some- 
times the  case,  either  timber  or  concrete  piles  should  be 
employed.  The  foundations  for  the  engine  must  be 
very  carefully  set  out,  and  the  holes  in  the  masonry 
left  for  the  anchor  bolts,  by  means  of  wooden  templates 
supporting  collapsible  wood  centres  or  wrought-iron 
pipes,  round  which  the  concrete  is  filled  in.  If  pipes 
are  used  and  it  is  desired  to  withdraw  them,  they  must 
be  kept  free  by  slight  movement  before  the  concrete 
sets.  If  solid-wood  centres  are  built  into  the  founda- 
tions for  anchor  bolts,  a  great  deal  of  trouble  and 
expense  is  required  to  burn  them  out  with  hot  irons. 
Nothing  can  surpass  the  dressed  stone  for  an  engine 
bed,  rubbed  down  to  a  perfectly  level  surface,  but 
the  usual  method  at  the  present  day  is  to  simply 
pack  up  the  bed  -  plate  and  fill  in  with  cement  or 
1  grout.'  It  is  of  importance  that  there  should  be  no 
delay  in  this  process  as  cement  sets  quickly,  and  the 
'  grout '  must  set  in  a  solid  mass  to  be  a  success. 
Only  the  very  best  brands  of  cement  should  be  used 
for  the  work. 

Boiler  foundations  are  often  too  shallow,  especially 
for  water -tube  boilers.  In  the  setting  for  these  boilers 
there  is  a  heavy  mass  of  masonry  over  a  small  area. 
Though  the  boiler  itself  takes  no  harm  from  some  settle- 
ment, the  steam  mains  are  strained  and  the  joints  will 
be  a  perpetual  source  of  trouble  from  leakage.  If  a 
serious  settlement  takes  place,  it  will  cause  fracture 
and  much  damage  may  result.  In  front  of  the  boilers 
ample  space  must  be  left  for  the  coal,  and  a  line  of  rails 
for  the  coal  trolley. 


152     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

VENTILATION. 

With  horizontal  engines  more  floor  space  is  required 
than  for  vertical  engines,  but  less  head  room.  In  the 
roof  ample  ventilation  must  be  provided.  The  venti- 
lators of  whatever  type  should  be  so  designed  as  to 
exclude  the  dust  as  much  as  possible.  Rows  of  large 
windows  are  both  unnecessary  and  objectionable,  but 
the  building  must  be  well  lighted.  In  dusty  countries 
much  injury  is  done  to  the  bearings  by  the  dust  coming 
through  the  open  windows.  If  the  internal  walls  are 
lined  with  glazed  bricks  an  excellent  effect  is  produced, 
but  some  authorities  do  not  care  to  go  to  this  expense. 

ENGINE-HOUSE  FLOOR. 

A  tiled  composite  floor  of  steel  joists  and  concrete 
will  meet  all  requirements,  but  immediately  round  the 
machinery  and  covering  all  flanged  pipes,  also  accessories 
in  the  basement,  cast-iron  chequered  floor-plates  should 
be  arranged.  They  must  be  supported  on  steel  joists, 
which  can  be  dismantled  without  interfering  with  the 
floor.  These  removable  plates  are  of  great  importance, 
as  they  not  only  admit  light  to  the  basement  when 
removed,  but  enable  any  section  of  the  machinery  to 
be  dismantled  without  expense  or  trouble.  Again,  oil 
dropping  from  the  valve  gear  is  easily  wiped  up,  which 
would  otherwise  leave  untidy  stains  on  the  tile  floor. 
Frequent  washing  of  the  floor  should  take  place,  and  a 
few  gratings  with  service  taps  for  hose  pipes  will  save 
a  great  deal  of  labour. 

STEAM  MAINS. 

The  engine  room  must  be  partitioned  off  from  the 
boiler  house,  and  the  boilers  themselves  so  situated 


POWER  HOUSE  153 

that  the  main  steam  pipes  are  as  short  as  possible.  All 
lengths  should  have  certain  points  to  which  they  drain, 
and  the  flanges  jointed  with  metallic  rings  if  superheated 
steam  is  used,  also  all  auxiliary  steam  piping  in  the 
engine  house  must  be  steel  pipe,  expanded  and  flanged. 
Ordinary  screw  joints  may  last  a  few  years,  but  sooner 
or  later  they  will  perish  and  leak  from  the  action  of 
the  superheated  steam. 

The  general  arrangement  and  erection  of  the  steam 
mains  is  of  great  importance,  as  it  is  practically  the  only 
section  of  the  plant  in  which  it  is  possible  for  an  explo- 
sion to  occur.  This  is  due  to  what  is  known  as  '  water 
hammer.'  It  is  a  problem  of  '  cause  and  effect.'  We 
know  the  effect,  but  the  cause  is  a  matter  of  conjecture. 

'  Water  hammer  '  is  the  result  of  admitting  steam  into 
a  pipe  partly  filled  with  water.  It  is  the  action  set  up 
by  an  elastic  fluid  containing  latent  heat,  when  it  is 
suddenly  brought  in  contact  with  an  inelastic  fluid. 

Undoubtedly  much  depends  on  the  arrangement  of 
the  steam  mains.  Some,  for  instance,  invite  the  pheno- 
menon, others  tend  towards  it,  while  it  would  be  rash 
to  assert  that  any  system  exists  where  it  is  impossible 
for  it  to  take  place.  Even  with  every  safeguard  and 
protection,  carelessness  and  ignorance  may  in  a  few 
minutes  bring  about  the  practical  destruction  of  an 
entire  section  which  has  been  regarded  beyond  reproach 
after  years  of  faultless  working.  Pressure  exerted  upon 
water  in  a  confined  space  is  equally  distributed  through- 
out the  whole  mass,  but  is  able  by  kinetic  energy  to 
exert  additional  force  in  the  direction  of  motion.  To 
attain  motion  its  inertia  has  to  be  overcome,  and  on 
coming  to  rest  its  momentum  has  to  be  resisted.  The 
more  suddenly  these  operations  are  performed,  the 
greater  is  the  pressure,  and  the  greater  is  the  resistance 


154     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

required.  Water  possesses  the  quality  of  minute  dis- 
integration, and  in  commercial  practice  there  is  no 
metal  which  is  not  porous  under  sufficient  pressure. 

Prevention  is  better  than  cure,  and  there  is  no  reason 
why  with  a  well-designed  system,  water  hammer  should 
occur  if  simple  precautions  are  taken.  In  the  first  place, 
as  already  stated,  steam  mains  should  be  erected  so 
they  drain  to  certain  points,  and  particular  care  must 
be  exercised  that  any  section  where  water  can  accumu- 
late is  provided  with  a  drain  of  ample  proportions 
besides  a  corresponding  valve  for  the  admission  of  air. 
Before  permitting  steam  to  pass  into  the  main,  these 
valves  must  be  opened  and  left  open  till  steam  is  emitted. 
However,  no  expenditure  on  accessories  or  automatic 
devices  will  avert  danger  if  they  are  not  assiduously 
attended.  The  provision  of  safeguards  is  worse  than 
useless  if  they  are  neither  understood  nor  operated  when 
the  occasion  arises.  In  fact,  they  are  speedily  reduced 
to  additional  dangers  in  the  system.  That  explosions 
and  disasters  are  not  more  frequent  is  entirely  due  to 
the  ability  and  care  of  those  who  control  the  power 
house. 

ACCESSORIES. 

Most  of  such  items  are  of  extremely  doubtful  value, 
and  the  purchaser  should  bear  in  mind  that  they  are 
made  to  sell  first  and  economise  afterwards. 

For  instance,  before  steam  traps  came  into  use,  steam 
jackets  were  efficiently  drained  by  a  water  sack.  When 
traps  are  new  and  in  good  working  order  they  save 
attention,  but  if  fixed  in  situations  where  superheated 
system  is  used  they  will  soon  leak.  Again,  traps  must 
work  equally  well  under  pressure  or  by  gravitation. 
There  are  also  useful  devices  known  as  oil  separators, 


I 

POWER  HOUSE  155 

but  it  must  not  be  assumed  they  remove  all  the  oil  in 
the  exhaust  steam.  Automatic  recorders  for  steam  and 
air  pressure  and  a  Venturi  meter  to  register  the  quantity 
of  discharged  air  are  useful  checks. 

There  are  also  devices  for  measuring  the  feed  water, 
draught  in  the  chimney,  and  the  volume  of  water 
circulated  through  the  condenser,  etc.,  and  it  would  be 
rash  to  assert  that  they  contribute  to  the  efficiency  of 
the  average  power  house  unless  they  are  all  carefully 
looked  after  and  the  records  kept  and  compared  and, 
in  fact,  the  condition  of  a  perpetual  trial  maintained. 

On  the  other  hand,  an  economiser  situated  in  the  flue 
for  heating  the  feed  water  does  effect  a  large  saving. 
The  feed  pumps,  as  a  rule,  discharge  the  water  from  the 
hot-well  tank,  which  should  be  above  the  level  of  the 
pump,  through  the  economiser. 

These  pumps  must  be  suitably  proportioned  for  supply- 
ing the  average  requirements  of  the  boiler.  If  too  large, 
great  difficulty  will  be  found  in  setting  them  to  run 
slow  enough,  especially  with  water-tube  boilers  at  an 
air-compressing  station,  as  the  demand  for  them  is 
irregular. 

WATER  SUPPLY. 

The  importance  of  an  ample  water  supply  of  good 
quality  for  an  air-compressing  station  cannot  be  over- 
estimated. Water  for  the  cooling  of  the  air-compressor 
jackets,  for  the  surface  condensers,  and  cooling  the  air 
intakes  is  required.  They  can  all  be  supplied  from  the 
same  pump  under  normal  conditions,  but  if,  for  some 
reason,  the  condenser  is  not  running  and  the  engine  is 
exhausting  to  atmosphere,  a  by-pass  from  the  town 
service  should  be  provided  for  the  compressor  jackets. 

The  source  from  which  the  water  is  taken  will  depend 


156     EFFICIENCY  OF  PUMPS  AND  EJECTOKS 

entirely  on  local  conditions ;  if  a  river  is  near  at  hand, 
it  is  obviously  the  best.  If  a  tube  well  has  to  be  sunk, 
make  sure  the  water  is  not  too  full  of  impurities,  or  heavy 
expense  will  be  incurred  on  repairs  to  boilers,  condensers, 
etc.  If  it  is  a  necessity  to  rely  on  the  town  supply 
entirely,  a  very  large  cooling  pond  should  be  provided. 
When  the  cooling  water  cannot  be  kept  below  90°  F., 
there  is,  no  doubt,  a  serious  loss  in  the  efficiency  of  the 
plant. 

Am  COOLER. 

In  the  compression  of  air,  heat  is  generated,  and  the 
more  efficient  are  the  arrangements  for  reducing  this 
temperature  the  more  efficiently  is  compression  carried 
out.  We  want  to  keep  the  compressor  cylinder  cool 
in  the  same  way  that  we  require  to  keep  the  steam 
cylinders  hot.  With  single  compressors  at  low  pressure, 
such  as  we  are  dealing  with,  the  loss  from  this  cause 
can  be  reduced  to  a  very  small  percentage :  first,  from 
circulating  cold  water  round  the  compressor  cylinder, 
and  secondly  from  drawing  cold  air  into  the  cylinders 
to  be  compressed.  In  summer-time  and  in  semi-tropical 
countries  an  air-cooling  device  at  the  intake  is  of  great 
value. 

It  usually  consists  of  a  circular  masonry  well,  above 
ground  level,  in  which  roofing  tiles  are  arranged  on  a 
suitable  frame,  and  the  bell  mouth  of  the  intake  termin- 
ates beneath  the  tiles.  On  these  tiles  water  incessantly 
drips  and  the  air  finds  its  way  through  the  roof.  The 
higher  the  atmospheric  temperature,  the  higher  the 
evaporation,  and  the  more  valuable  is  the  device  for 
cooling  the  air  before  being  drawn  into  the  compressors. 
It  also  effectually  prevents  dust  entering  with  the  air. 

Plate  XX.  shows  the  difference  in  temperature  of  the 


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158     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

atmosphere  and  the  air  in  the  intake  duct  of  the  com- 
pressor after  being  cooled.  It  will  be  observed  that 
from  4  P.M.  to  6  P.M.  the  atmospheric  temperature  was 
105°  F.  and  in  the  duct  90°  F.,  a  drop  of  no  less  than 
15°  F.  With  the  fall  in  temperature  the  difference 
decreases  till  at  7  A.M.  evaporation  ceases. 

The  temperature  in  the  Venturi  meter  tube  is  the 
temperature  of  the  compressed  air  before  it  enters  the 
distributing  main.  In  this  case  the  figure  given  on  the 
diagram  has  probably  little  to  do  with  the  temperature 
at  which  the  air  leaves  the  compressor,  as  it  passes 
through  two  large  steel  receivers  exposed  to  the  sun, 
and  the  temperature  of  the  air  in  this  receiver  which 
discharges  through  the  Venturi  tube  depends  upon  the 
atmosphere  above  90°  F. 

VOLUME  OF  AIR  TO  RAISE  SEWAGE. 

The  next  six  diagrams,  Plates  XXI. -XXVI.,  merit 
very  close  attention  from  those  who  are  hesitating 
between  pumps  and  ejectors  on  the  score  of  air-main 
leakage. 

The  diagrams  cover  a  period  of  three  years  and  show 
the  volume  of  sewage  raised  each  month,  the  air  pres- 
sure maintained,  and  the  volume  of  air  at  that  pressure, 
required  to  raise  one  gallon  of  effluent,  by  the  Cairo  Main 
Drainage  Ejector  system. 

The  ejector  discharge  diagrams,  XXI.,  XXIII.,  XXV., 
give  the  month  and  year  on  the  first  line,  the  total 
volume  raised  in  metric  tons  (cub.  metres)  per  month, 
and  the  figures  in  the  left-hand  column  are  100,000. 
Thus  *  980 '  stands  for  980,000  cub.  metres,  and  the 
lowest  figure  '300'  stands  for  300,000  cub.  metres, 
Plate  XXV. 

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160    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

water  diagrams,  XXII.,  XXIV.,  XXVI.,  show  the  date 
and  month  in  the  first  line,  and  immediately  below  each 
month  the  volume  of  air  required  to  raise  one  gallon. 
Thus  '0'713'='713;  or  nearly  three-quarters  of  a  cubic 
foot  of  free  air  is  required  to  raise  one  gallon  of  water  to 
a  height  in  feet  equal  to  22*10  Ibs.  pressure  per  square 
inch.  The  left-hand  column  of  figures  shows  fractions  of 
a  cubic  foot  between  0'44  at  the  bottom  and  0*78  at  the 
top,  and  the  upper  curve  takes  its  course  from  these  figures. 

The  lower  dotted  curve  represents  Ibs.  pressure  of 
air  per  square  inch.  The  bottom  line  of  figures  shows 
the  average  pressure  of  air  maintained  each  month, 
and  the  right-hand  column  of  figures  show  fractions  of  a 
pound  from  20  Ibs.  at  the  bottom  to  26*8  Ibs.  at  the 
top. 

Thus  the  top  and  left-hand  column  figures  (air  volume) 
refer  to  the  upper  curve.  The  bottom  and  right-hand 
column  of  figures  (air  pressure)  refer  to  the  lower  dotted 
curve. 

Plates  XXI.,  XXIII.,  XXV.  show  the  variation  of 
the  inflow  to  the  ejector.  The  great  difference  between 
April  and  October  is  due  to  the  rising  of  the  Nile,  which 
raises  the  level  of  the  subsoil  water  and  this  percolates 
into  the  sewers.1  The  subsoil  of  Cairo  is  for  the  greater 
part  a  sandy  loam,  and  any  rise  in  the  level  of  the  river 
is  faithfully  reflected  in  the  subsoil  percolation. 

Plates  XXII.,  XXIV.,  XXVI.  show  the  air  pressure 
and  the  volume  of  air  in  cubic  feet  to  raise  one  gallon 
of  sewage  at  a  head  in  feet  equal  to  the  pressure  given. 

In  studying  the  diagrams  they  must  be  read  together, 
and  what  has  been  previously  stated  in  Chapter  III., 
relative  to  proportional  air-main  leakage,  will  be  fully 
appreciated.  That  is  to  say,  the  greater  the  volume 

1  See  Subsoil  of  Cairo,  by  E.  C.  B.  S. 


9  to 


Li 


§68 


164     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

raised  the  less  is  the  proportional  leakage,  and  the  lower 
the  air  pressure  maintained  the  greater  the  volume 
raised  for  a  given  quantity  of  air. 

This  is  beautifully  illustrated  in  Plates  XXIII.  and 
XXIV.,  November  1917.  Though  October  shows  the 
greatest  volume  raised  and  took  0*494  cubic  feet  of  free 
air  at  22*5  Ibs.  to  raise  one  gallon,  November  shows  a 
better  result  with  0*471  cubic  feet  of  free  air  per  gallon,  as 
the  air  pressure  was  lower  at  22*40  Ibs.  per  square  inch. 

Again,  the  reduction  in  volume  of  air  required  to  raise 
a  given  quantity  of  sewage  is  well  shown  in  Plate  XXVI. 
for  the  month  of  March  1919.  In  January  1919  (Plate 
XXVI.)  the  drop  in  the  volume  of  air  and  increased 
pressure  was  due  to  exceptional  rain.  The  air  figure 
is  high  owing  to  having  maintained  25  Ibs.  air  pres- 
sure for  several  days.  If  the  air  pressure  had  not 
exceeded  22  Ibs.,  the  volume  curve  would  show  a  much 
larger  drop. 

The  volume  figures  for  May  and  August  1916  (Plate 
XXII.)  are  the  result  obtained  on  official  trials.  For 
the  month  of  March  1917  (Plate  XXII.)  the  volume  of 
air  required  was  0*628  cubic  foot,  while  for  March  1919 
(Plate  XXVI.)  it  was  0*639  cubic  foot  to  raise  one  gallon. 
It  is  true  the  volume  of  water  raised  is  greater,  but  con- 
sidering in  1919  air  was  being  used  for  auxiliary  pur- 
poses, laboratory  work,  and  burning  oil  under  steam 
boilers,  the  increase  in  leakage  from  the  air  main  is 
extremely  small.  And  it  must  be  remembered  that 
during  this  period  practically  no  ppening  up  or  recaulk- 
ing  of  the  mains  had  taken  place.  It  is  obvious  that 
there  is  no  reason  why  excessive  leakage  in  an  air-main 
system  should  exist  if  the  work  is  carried  out  under 
competent  supervision. 

In  cases  where  a  greater  volume  of  water  is  raised,  but 


166     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

the  volume  of  air  is  also  greater  instead  of  less,  the  extra 
pressure  will  account  for  this  result.  On  the  other  hand 
(see  Plates  XXIII.  and  XXIV.,  September  1917),  the 
extra  volume  of  water  is  so  large  as  to  still  show  a  less 
volume  of  air  per  gallon,  though  an  extra  pound  pressure 
was  maintained. 

These  diagrams  confirm  the  ejector  efficiency  curve 
shown  on  Plate  XII.,  page  58.  They  are,  indeed,  of 
more  value  on  which  to  base  conclusions  than  many 
pages  of  laboured  explanation,  multitudes  of  figures,  and 
all  the  minute  details  of  an  official  trial,  as  we  see  here 
what  is  actually  done  in  daily  work,  and  not  what  an 
installation  ought  to  do. 

ECONOMY  IN  RUNNING  PLANT. 

In  running  an  air-compressing  plant  for  an  ejector 
system  with  fluctuating  conditions  of  speed  and  pres- 
sure, it  is  not  possible  to  obtain  so  high  an  efficiency  as 
with  a  pumping  engine  delivering  against  a  constant 
head  of  water. 

With  low  pressure  and  low  speed  the  various  forms  of 
automatic  governor  effect  little  saving,  as  the  principal 
loss  takes  place  in  firing  the  boilers  to  meet  a  constantly 
fluctuating  demand. 

The  economy  of  the  plant  will  depend  on  the  intelli- 
gence, ability,  and  vigilance  of  the  fireman  more  than 
any  other  member  of  the  staff.  Assuming  he  has  water- 
tube  boilers,  the  feed  pump  must  be  set  to  give  a  con- 
stant water  level,  his  dampers  and  ashpit  doors  adjusted 
frequently,  and  only  suitable  opportunity  taken  for 
cleaning  his  fires. 

FUEL. 

For  the  generation  of  steam  we  have  in  order  of  heating 


168     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

value  oil  firing,  coal  firing,  and  rubbish  firing.  There 
is  also  a  system  of  vegetable -refuse  firing  by  first  con- 
verting it  into  gas  and  conveying  the  gas  directly  to 
the  furnace.  In  countries  where  oil  is  cheap — that  is, 
fuel  oil  or  residues  from  the  refineries — ordinary  boiler 
furnaces  may  be  adapted  to  steam  or  air- jet  burners  with 
little  trouble  and  expense. 

Though  oil  firing  is  practically  unknown  in  England, 
it  is  largely  used  in  the  East,  particularly  in  many  places 
where  ejectors  are  already  installed  or  could  be  installed 
with  advantage. 

OIL  FIRING  WATER- TUBE  BOILERS. 

Plates  XXVII.,  XXVIII.  show  respectively  a  front 
elevation  and  section  of  a  battery  of  Babcock  and 
Wilcox  water -tube  boilers  of  800  horse -power  approx. 
which  have  been  converted  from  coal  to  oil  firing.  They 
are  used  for  supplying  the  Cairo  air -compressing  engines 
with  steam.  Steam  is  used  for  the  atomising  fluid,  as 
though  air  gives  a  higher  efficiency,  the  local  bricks 
fail  to  stand  the  intense  heat.  With  oil  firing  it  is 
possible  to  run  two  compressing  plants  from  one  boiler, 
whereas  with  coal  this  cannot  be  done. 

The  position  of  the  ejector,  pipes,  and  feed  tank  has 
been  arranged  with  a  view  to  securing  the  maximum 
efficiency  in  working  and  economy  in  construction. 

The  essential  features  are  : 

1.  Simple  and  reliable  apparatus  for  raising  the  oil 

from  the  storage  tank  to  the  feed  heating  tank. 

2.  Arranging  the  feed  tank  and  all  pipework  in  such 

a  way  that  all  boiler  brickwork,  flues  and  econo- 
misers,  etc.,  can  be  rebuilt  without  interfering 
with  the  installation. 


170     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

3.  The  efficient  heating  of  the  oil,  so  that  the  highest 
temperature  is  attained  as  the  oil  arrives  at 
the  boiler. 

The  oil  flows  from  the  storage  tank  a  by  means  of 
two  pipes,  controlled  by  stop  valves,  to  the  50-gallon 
ejector  d  located  in  the  adjoining  chamber  6,  at  such  a 
level  that  the  tank  can  be  completely  emptied. 

The  ejector  is  of  the  automatic  Shone  type,  operated 
by  compressed  air  from  the  main  at  22  Ibs.  the  square  inch. 

The  oil  passes  up  the  discharge  pipe  F  through  a  stop 
valve  g  to  the  feed  heating  tank  h,  supported  on  cast-iron 
pillars,  and  located  in  such  a  position  that  there  is  an 
equal  distribution  to  the  four  boilers  through  a  minimum 
length  of  pipe.  This  tank  is  at  such  a  level  as  to  give  a 
suitable  velocity  to  the  oil  in  the  feed  pipe,  and  manipula- 
tion of  the  stop  valve  o  and  interchangeable  strainer  n 
from  the  existing  boiler  stage. 

The  feed  tank  contains  a  steam  coil  for  heating  the 
oil,  and  a  drain  pipe  i  carried  through  the  bottom  of  the 
tank,  controlled  by  a  steam  trap  ./  for  preventing  the 
accumulation  of  water  in  the  steam  coil,  and  the  pipe  k 
enables  the  tank  to  be  emptied  of  oil,  or  during  use 
to  drain  off  any  water  which  may  accumulate.  A 
suitable  float  and  guide,  with  pulley  attachment  and 
indicator  board,  is  also  provided  for  showing  the  quantity 
of  oil  the  tank  contains.  A  distributing  plate  is  also 
fixed  in  the  tank,  beneath  the  oil  inlet,  in  order  to  prevent 
the  cold  oil  from  plunging  to  the  bottom. 

The  steam  for  heating  the  coil  is  taken  from  a  valve 
cover,  or  other  suitable  point  on  the  steam  main  which 
is  common  to  all  four  boilers,  and  by  means  of  a  gland 
and  stuffing-box  expansion  joint  passes  through  the 
bend  of  the  oil  main. 


172     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

Immediately  below  the  bend  is  fixed  a  strainer  con- 
trolled by  a  stop  valve,  and  as  the  straining  medium  is 
attached  to  the  cover  of  the  strainer  it  can  be  removed 
and  replaced  by  a  spare  cover  kept  for  the  purpose 
while  the  boiler  is  working.  By  this  arrangement  a 
single  tank  and  coil  is  sufficient  for  four  boilers,  the 
duplication  of  pipes  and  valves  is  avoided,  and  any  one 
of  the  four  boilers  can  be  started  up  at  a  few  minutes' 
notice. 

Weight  for  weight  there  is  a  saving  of  35  per  cent,  over 
coal,  a  saving  in  transport,  and  a  great  saving  in  labour. 
Under  steady  conditions  of  running  such  as  pumping 
water  under  a  constant  head,  the  economy  of  oil  firing 
is  more  apparent  than  when  applied  to  an  ejector  power 
station. 

For  the  sake  of  economy  in  the  consumption  of  air 
only  the  minimum  pressure  is  maintained.  Compressed 
air  is  extremely  sensitive  to  any  alteration  in  pressure, 
and  water -tube  boilers  are  also  extremely  sensitive 
under  oil  firing.  The  result  is  we  have  two  highly 
sensitive  powers  balanced  one  against  the  other,  and 
it  requires  experience  and  vigilance  on  the  part  of  the 
boiler  attendant  to  keep  them  in  a  state  of  equilibrium. 

Though  the  water -tube  boilers  may  not  be  quite  so 
economical  as  the  Lancashire  type  under  normal  condi- 
tions, they  lend  themselves  more  readily  to  the  rapid 
generation  of  steam  in  case  of  rain,  which  is  of  first 
importance.  Whether  coal  or  oil  firing  should  be  recom- 
mended is,  of  course,  purely  a  matter  of  the  price  and 
supply  at  which  these  fuels  can  be  obtained. 

GAS  FIRING. 

Owing  to  the  extremely  high  prices  of  these  fuels 
that  have  recently  prevailed,  boilers  fired  with  gas  have 


POWER  HOUSE  173 

been  suggested.  Experimental  work  has  shown  that  it 
is  perfectly  feasible,  and  economical  results  have  been 
obtained. 

The  nature  of  the  material  is  of  no  consequence. 
Fallen  leaves,  straw,  sticks,  sweepings,  and  vegetable 
refuse  of  all  descriptions  are  fed  into  a  suitable  pro- 
ducer, and  the  gas  issues  directly  to  the  furnace.  To 
burn  such  material  a  large  grate  area  would  have  to  be 
provided,  and  difficulty  would  be  experienced  in  keep- 
ing up  the  steam. 

However,  when  analysing  the  high  efficiencies  obtained 
by  this  method  of  steam  generation,  the  capital  cost  and 
labour  must  be  carefully  taken  into  account.  It  takes 
many  tons  of  vegetable  fuel  to  equal  a  single  ton  of  oil 
or  even  coal,  and  in  place  of  a  single  man  to  attend  the 
boiler  we  have  a  number  of  men  engaged  in  handling 
the  rubbish,  and  raising  it  10  or  12  feet  to  charge  the 
producers.  All  such  labour  must,  of  course,  be  deducted 
from  the  power  of  the  engine  if  we  wish  to  compare 
results. 

Fuel  oil  is  the  most  concentrated  form  of  fuel  for 
firing,  and  the  expenses  connected  therewith  are  the 
smallest.  Rubbish  firing,  whether  by  dust  destructor  or 
by  first  converting  it  into  gas,  is  the  most  laborious,  and 
though  the  cost  of  the  oil  is  more  by  hundreds  per  cent, 
the  subsidiary  expenses  and  addition  to  plant  for  burn- 
ing rubbish  may  completely  wipe  out  the  difference. 


CHAPTER  X 
IMPROVEMENTS 

REASONS  FOB  INEFFICIENCY. 

FROM  the  preceding  chapters  it  is  clear  that  from  what- 
ever point  of  view  pumps  and  ejectors  are  considered, 
the  mechanical  efficiency  of  the  reciprocating  pump  is 
far  superior  to  that  of  the  pneumatic  ejector. 

On  the  other  hand,  the  merits  of  the  pneumatic  ejector, 
as  an  apparatus  for  raising  crude  sewage,  are  so  obvious 
that  methods  of  improving  their  efficiency  are  worth 
some  consideration.  To  spend  time  and  money  on  ob- 
taining an  extra  1  per  cent,  or  2  per  cent,  efficiency  on 
the  reciprocating  pump,  when  we  already  have  an  effi- 
ciency of  90  per  cent,  compared  to  40  per  cent,  of  the 
ejector,  is  misdirected  energy.  There  is  room  for  very 
little  improvement  in  the  pump,  but  for  a  great  deal 
in  the  pneumatic  ejector. 

Before  discussing  possible  means  of  improvement,  let 
us  first  briefly  enumerate  the  reasons  why  the  ejector 
is  so  inefficient  from  the  mechanical  point  of  view. 
The  reasons  are  as  follows  : 

1.  The  ejector  is  operated  by  a  secondary  power. 

2.  There  is  a  certain  amount  of  unavoidable  loss  in 

the  compression  of  air. 

3.  The  air  is  used  in  the  ejector  without  expansion; 

there  is  no  '  cut  off.' 

4.  The  loss  of  leakage  from  air  mains. 

174 


IMPROVEMENTS  175 

5.  Great  variation  in  the  volume  of  air  required. 

6.  Absence  of  storage. 

7.  Fluctuation  in  pressure. 

8.  Absence  of  uniform  running  conditions. 

If  there  is  an  average  loss  of  6  per  cent,  or  7  per  cent, 
from  each  of  the  above  causes,  it  is  easy  to  see  that  in 
the  aggregate  they  mount  up  to  a  large  figure ;  and 
again,  that  the  opportunity  for  leakage  and  loss  is  multi- 
plied a  hundredfold  in  such  a  system  as  compared  to 
the  simple  process  of  direct  pumping.  Therefore  it 
may  be  said,  as  far  as  the  mechanical  efficiency  is  con- 
cerned, the  ejector  will  never  equal  the  pump  in  prac- 
tice. But  that  is  no  reason  why  we  should  not  endeavour 
to  improve  the  ejector  or  accept  the  low  efficiency  as 
a  permanent  argument  against  its  installation. 

It  has  been  clearly  shown  in  raising  crude  sewage  there 
are  other  merits  of  such  a  nature  that  they  are  of  equal 
importance,  and  as  much  responsible  for  the  yearly 
maintenance  costs  as  the  mechanical  efficiency.  Before 
proceeding,  it  must  be  particularly  pointed  out  that 
the  object  of  improving  ejectors  is  to  increase  their 
efficiency  without  the  expenditure  of  a  single  additional 
penny  on  motive  power,  and  to  such  an  extent  that  any 
increased  costs  in  other  directions  still  leave  a  sufficiently 
high  percentage  of  improvement  to  be  a  commercial 
proposition. 

To  be  convincing  it  is  necessary  to  be  logical.  There- 
fore we  must  proceed  step  by  step  to  show  how  the 
efficiency  may  be  improved,  and  it  is  as  well  first  of 
all  to  touch  on  some  of  the  elementary  aspects  of  the 
problem.  Let  us  analyse  each  cause  of  loss  and  ascertain 
from  which  it  is  easiest  to  eliminate  or  reduce  that  loss 
which  takes  place,  or  whether  some  modification  to 


176     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

the  general  arrangement  of  the  system  or  alteration  in 
the  running  conditions  would  bring  about  that  desir- 
able end. 

IMPROVEMENTS  SUGGESTED. 

Referring  to  reasons  Nos.  1  and  2,  in  discussing  the 
merits  of  a  secondary  power  and  the  apparatus  in  which 
it  performs  its  work,  it  is  difficult  to  exclude  the  original 
source  and  generation  of  the  prime  power,  as  the  con- 
version of  one  power  to  another  and  its  medium  of 
transmission  contribute  so  largely  to  the  ultimate  effi- 
ciency of  the  system  ;  and  in  referring  to  the  efficiency 
of  ejectors  we  must  include  the  whole  system.  Thus 
if  the  generation  of  the  prime  power  is  inefficient,  the 
loss  has  to  be  borne  by  the  apparatus  that  does  the 
work  in  the  balance  sheet  of  power  employed  and  work 
done. 

By  using  a  secondary  power  some  loss  cannot  be 
avoided,  no  matter  what  that  power  is,  but  the  greater 
the  power  the  less  is  the  loss  in  proportion.  An  air 
compressor  is  an  engine  of  unevenly  distributed  resist- 
ance. There  is  loss  from  clearance,  loss  from  heating 
of  the  air  during  compression,  but  with  a  first-class 
machine  and  well-cooled  cylinders  and  a  pressure  of  only 
20  Ibs.  and  30  Ibs.  the  loss  is  exceedingly  small,  and  it 
is  doubtful  if  there  is  anything  to  be  gained  by  experi- 
mental work  or  '  improvements  5  in  this  direction. 

COMPRESSED  AIR:   LATENT  POWER. 

Reason  No.  3  offers  by  far  the  widest  field  for  improve- 
ment and  merits  some  discussion.  It  is  well  known 
the  efficiency  of  compressed  air  as  a  secondary  motive 
power,  when  used  in  a  suitable  mechanical  apparatus, 
is  little  inferior  to  that  of  steam.  Comparatively  speak- 


IMPROVEMENTS  177 

ing,  it  can  be  stored.  Needless  to  say,  this  is  a  great 
advantage.  It  is  as  well  to  bear  in  mind,  science  tells 
us,  '  the  power  which  is  contained  in  any  volume  of  air 
at  a  given  pressure  is  dependent  on  its  distance  in  tempera- 
ture above  the  absolute  zero,  and  that  there  is  as  much 
power  in  a  pound  of  air  at  15  Ibs.  the  square  inch  (gauge 
press.)  and  at  60°  F.  as  there  is  in  one  pound  of  air  at 
100  Ibs.  the  square  inch  (gauge  press.)  and  at  60°  F.' 
But,  of  course,  the  energy  available  for  useful  work  is 
much  greater  in  the  higher  pressure. 

Again,  as  to  the  application  of  compressed  air  to 
ejectors  :  '  The  volume  of  one  pound  of  air  at  30  Ibs. 
the  square  inch  (gauge  press.)  and  at  80°  F.  equals 
4' 41 2  cubic  feet,  and  the  greatest  amount  of  work  it 
can  do  in  an  ejector  is  19,060  foot-lbs.  But  the  same 
quantity  of  air  under  adiabatic  expansion  could  yield 
27,405  foot-lbs/  The  significance  of  this  cannot  be  over- 
stated and  must  not  be  lost  sight  of. 

COMPOUNDING  EJECTORS. 

To  re-use  the  air  in  the  ejector,  or  use  it  expansively 
would,  without  doubt,  be  a  great  improvement.  In  the 
compound  steam  engine  the  motive  power,  after  per- 
forming work  in  one  cylinder,  is  admitted  to  another  of 
greater  volume,  in  which  it  continues  to  do  useful  work 
till  nearly  the  whole  of  the  available  pressure  is  extracted 
from  the  steam.  The  motive  power  is  directly  re -used 
in  the  engine,  with  the  result  that  a  degree  of  economy 
is  attained  which  is  quite  unknown  in  the  pneumatic 
ejector.  By  duplicating  the  cylinders  and  reciprocat- 
ing parts  we  practically  double  the  useful  work  per- 
formed in  the  conversion  of  steam  to  mechanical  power, 
the  reciprocating  parts  and  the  flywheel  (if  there  happens 
to  be  one)  by  means  of  kinetic  energy  largely  contribut- 

M 


178     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

ing  to  this  result.  But  in  dealing  with  a  liquid  it  is 
particularly  difficult  to  make  the  fullest  use  of  the  expan- 
sive power  of  the  motive  fluid  as  an  even  pressure  has 
to  be  maintained  throughout  the  stroke  by  the  steam, 
if  we  do  not  provide  some  type  of  compensating  attach- 
ment for  the  storage  of  the  energy  used  in  the  motive 
cylinder. 

As  already  stated,  the  ejector  has  neither  rotary  nor 
reciprocating  parts ;  the  motive  power  is  the  piston  or 
impeller.  The  ejector  will  admit  and  discharge  sticks, 
stones,  bags,  bottles,  metal,  rubbish  and  solid  matter 
of  every  description  continually  without  injury,  and 
requires  no  screening  of  the  sewage.  To  introduce 
rotary  or  reciprocating  parts  to  an  ejector  or  bring  them 
in  contact  with  the  liquid  at  once  destroys  the  utility 
and  perfection  of  the  apparatus.  Hence  we  cannot 
store  the  energy  of  the  motive  fluid  and  use  it  expan- 
sively by  the  usual  methods.  In  compressed  air  we  are 
using  an  ideal  motive  power.  In  fact,  we  have  at  our 
disposal  a  gas,  elastic  and  non-explosive,  and  theoreti- 
cally, according  to  science,  capable  of  giving  out  as  much 
work  as  is  expended  upon  it.  Yet  with  this  remarkable 
motive  fluid  we  find  the  pneumatic  ejector  in  the  lowest 
ranks  of  mechanical  efficiency — principally  for  this 
reason :  the  immense  expansive  power,  the  latent  force, 
the  intrinsic  energy  of  the  air  itself,  is  absolutely  wasted. 

In  fact,  as  far  as  motive  power  is  concerned  for  dis- 
charging the  ejector,  we  might  as  well  be  using  water,  a 
solid  '  dead  power  '  which  is  dependent  on  kinetic  energy 
alone  without  latent  power.  The  discharging  of  the 
effluent  from  the  ejector,  as  before  remarked,  is  the  work 
the  compressed  air  has  to  do,  and  it  is  obvious  from  the 
construction  of  the  apparatus  that  the  volume  of  air 
must  be  maintained  throughout  the  whole  of  this  opera- 


IMPROVEMENTS  179 

tion  at  a  certain  pressure  to  raise  the  water  to  the  required 
height. 

EXHAUST:  WASTE  OF  POWER. 

Therefore  it  follows  that  at  the  end  of  the  discharge  a 
volume  of  compressed  air  at  full  pressure  fills  the  body 
of  the  ejector  in  place  of  the  liquid  expelled.  The  exhaust 
valve  opens  and  the  whole  of  this  *  power  '  is  discharged 
into  the  atmosphere  without  restraint,  a  power  equal 
to  the  entire  energy  of  the  motive  fluid  being  treated  as 
a  mere  *  waste  product  '  of  the  machine. 

It  is  indeed  the  liberation  of  a  mechanical  agent  under 
full  control,  from  which  we  have  neither  extracted  the 
energy  nor  reduced  its  capabilities  for  further  work. 

It  is  this  '  waste  product,'  the  exhaust  from  the  ejector, 
that  it  is  possible  to  make  use  of  either  by  using  it  as 
a  motive  power  for  recompressing  a  certain  percentage 
of  its  own  volume  to  assist  the  next  discharge,  or  return- 
ing the  exhaust  to  the  power  house  and  recompressing 
the  air.  For  the  exhaust  air  to  recompress  a  percen- 
tage of  its  own  volume  to  assist  the  next  discharge  would 
be  the  most  economical  in  a  multiple  ejector  system, 
but  at  the  lower  pressures  the  motors  would  have  to 
be  an  unwieldy  size.  The  distinctive  characteristics  of 
such  a  motor  are  :  the  pressure  air  flows  through  the 
engine  when  the  pressure  falls  below  a  predetermined 
value,  and  that  upon  the  pressure  rising  above  such  a 
value  the  necessary  exhaust  ports  are  closed  and  the 
engine  started  ;  a  rotary  cam  shaft  to  which  is  auto- 
matically imparted  a  lateral  motion  by  means  of  a  spring- 
controlled  piston  and  cylinder,  operated  by  the  motive 
fluid,  which  drives  the  engine  for  the  purpose  of  starting 
and  stopping  the  motor. 

The  air  and  exhaust  valves  of  an  ejector  installation 


180     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

owe  their  reliability  to  what  is  known  as  '  pneumatic 
control.'  Comparatively  speaking,  there  is  nothing  to 
wear  out  and  nothing  to  go  wrong.  No  levers,  no  links, 
no  pins,  a  few  lengths  of  small  tubing  and  the  thing  is 
done  how  and  where  we  like.  Needless  to  say  it  is  a 
simple  matter  to  adapt  such  a  system  to  control  the  air 
motor  compressor  in  such  a  manner  as  to  make  it  as 
automatic  in  action  as  the  ejectors  themselves,  and  at 
the  same  time  safeguard  their  own  continuous  working. 

The  principal  characteristics  of  such  a  system  of 
control  are  :  the  application  of  a  valve,  termed  the 
differential  exhaust  valve,  which  is  capable  of  taking 
up  one  of  two  positions  for  the  purpose  of  arresting  the 
discharge  of  the  exhaust  directly  to  the  atmosphere  ; 
the  application  of  a  valve,  termed  the  intercepting  valve, 
to  either  ejector  for  the  purpose  of  delaying  the  action 
of  the  differential  exhaust,  to  enable  one  ejector  to  be 
discharging  while  the  other  is  exhausting  to  the  motor 
compressor,  an  arrangement  of  operating  pipes  which 
enables  the  action  of  the  above  valves  to  be  entirely  con- 
trolled by  the  rise  and  fall  of  the  liquid  in  the  ejector 
body. 

It  must  not  be  supposed  that  it  would  be  worth  while 
compounding  ejectors  by  such  means  at  every  ejector 
station  in  a  large  system,  as  in  many  cases  small  ejectors 
will  not  discharge  more  than  a  few  thousand  gallons  per 
day,  and  the  cost  of  the  air  saved  would  not  equal  the 
extra  expenditure  and  maintenance.  In  large  stations, 
however,  discharging  half  a  million  gallons  per  day  and 
upwards  at  a  pressure  of  not  less  than  25  Ibs.  the  square 
inch,  a  real  increase  in  efficiency  would  undoubtedly  be 
effected  without  additional  expenditure  in  motive  power. 
The  higher  the  pressure  the  greater  the  value  of  utilising  the 
exhaust  air,  and  there  appears  to  be  no  reason  why  any 


IMPROVEMENTS  181 

pressure  up  to  single  compression,  say  60  to  70  Ibs.  the 
square  inch,  should  not  be  used  economically  by  such 
means  for  raising  crude  sewage.  Such  an  increase  in  pres- 
sure would  bring  the  ejector  within  range  of  the  majority 
of  sewage  schemes. 

OBJECTIONS  TO  COMPOUNDING  EJECTORS. 

Objections  have  been  raised  against  using  the  body 
of  the  ejector  as  an  air  receiver,  as  it  prevents  the  ejector 
from  being  used  at  the  maximum  capacity  in  abnormal 
times,  such  as  heavy  floods.  With  the  simple  ejector, 
the  exhaust  opens,  the  air  escapes  at  once,  and  the  water 
fills  the  ejector  against  the  atmosphere  at  the  maximum 
rate  permissible  by  the  size  of  the  inlet  pipes.  If  the 
ejector  is  used  as  a  receiver,  the  water  would  only  fill 
the  ejector  as  the  air  pressure  was  reduced — that  is  to 
say,  the  action  of  the  ejector  would  be  delayed  half  a 
minute  or  other  predetermined  time.  Therefore  in  time 
of  flood  if  the  maximum  rate  of  working  was  required 
under  such  conditions,  the  '  capacity '  of  the  ejector 
station  would  be  reduced — in  other  words,  would  not  be 
able  to  deal  with  so  large  a  volume  of  water  in  a  given 
time.  But  in  the  application  of  the  differential  exhaust 
valve  mentioned  above,  provision  has  been  made  so 
that  the  ejector  can  return  to  simple  working  at  any 
desired  moment  and  the  full  capacity  made  use  of. 
In  normal  times  the  average  ejector  does  not  work  at 
more  than  half  its  capacity.  In  fact,  whether  it  is  a 
pump  or  an  ejector,  a  large  reserve  must  always  be  pro- 
vided in  raising  sewage. 

Within  recent  years  motors  and  turbines  of  all  descrip- 
tions have  been  brought  to  a  high  state  of  perfection,  and 
what  would  have  been  an  4  extravagant  proposition  '  ten 
or  fifteen  years  ago  is  now  regarded  as  everyday  practice. 


182     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

To  utilise  compressed  air  in  turbines  or  motors,  a 
much  more  expensive  class  of  machinery  is  required  than 
for  an  ejector,  but  if  the  gain  in  efficiency  is  of  sufficient 
magnitude  there  is  no  reason  why  the  exhaust  should 
not  be  used.  No  doubt  the  exhaust  would  have  to  pass 
through  a  filter,  but  the  grease  and  grit  now  carried  up 
by  the  sudden  release  of  the  air  would  be  absent  under 
steady  conditions. 

As  a  rule,  ejectors  are  in  the  hands  of  corporations  and 
municipalities.  They  are  completely  out  of  sight  and 
from  one  year  to  another  their  existence  is  unknown, 
except  to  the  man  who  attends  them.  There  is  no  in- 
centive to  improvement  as  long  as  they  perform  their 
work,  as  their  maintenance  is  paid  for  by  the  ratepayers, 
and  the  rate  for  sewerage  is  looked  upon  as  an  unavoid- 
able burden  which  cannot  be  reduced.  But  of  recent 
years  the  ejector  has  been  adopted  by  many  firms  for 
draining  large  factories,  and  there  is  little  doubt  that 
those  who  have  had  actual  experience  of  their  working 
are  fully  alive  to  their  great  merits  compared  to  low-lift 
pumps  which  would  otherwise  be  installed  for  such 
purposes. 

RECOMPRESSING  THE  EXHAUST. 

There  is  another  method  of  recompressing  the  exhaust 
from  the  ejector,  by  returning  the  air  to  the  power  house. 
Provided  there  is  only  a  short  length  of  exhaust  main 
from  the  ejector  to  the  power  house,  this  is  an  admir- 
able plan,  and  has  given  some  excellent  results  in  prac- 
tice ;  but  the  writer  is  not  aware  that  it  has  been  tried 
on  an  extensive  scale.  Indeed,  an  efficiency  of  64  per 
cent,  has  been  claimed  under  suitable  conditions.  There 
seems  to  be  no  reason  why  such  a  system  should  not 
be  applied  to  a  large  super-ejector  station,  when  there 


IMPROVEMENTS  183 

are  no  air  mains,  and  even  higher  efficiency  obtained. 
With  a  multiple  system,  however,  scattered  over  a  large 
area,  the  extra  expense  of  duplicate  mains  would  be  a 
heavy  item  in  first  cost,  and  the  maintenance  of  the  air 
mains  would  be  doubled.  It  is,  though,  just  one  of 
those  improvements  that  can  be  applied  in  certain 
localities  that  is  worth  careful  consideration. 

It  must  not  be  forgotten  that  the  larger  the  station  is 
— that  is,  the  greater  the  power  employed — the  better  are 
the  results,  and  those  who  only  judge  efficiencies  from 
experience  with  small  powers  are  working  at  a  disad- 
vantage. 

Of  all  power  schemes  an  ejector  system  is  probably 
the  most  unsuitable  to  obtain  a  high  mechanical  effi- 
ciency, owing  to  the  comparatively  intermittent  nature 
of  the  work  and  the  small  power  employed. 

EXPANSION  OF  Am  IN  THE  EJECTOR. 

A  third  way  of  improving  the  efficiency  of  the  ejector 
is  by  using  the  air  expansively  in  the  ejector  body 
— that  is,  by  applying  a  valve  to  cut  off  the  air  when  a 
certain  volume  has  passed  into  the  ejector.  Probably 
more  time  and  money  have  been  expended  in  attempt- 
ing improvements  in  this  direction  than  in  any  other. 
It  entails  the  smallest  capital  outlay  and  would  be  a 
direct  saving. 

The  end  in  view — expansive  working  of  the  motive 
fluid — is  most  desirable,  but  the  means  of  carrying  it  out 
are  subject  to  certain  difficulties.  It  is  just  one  of  those 
improvements  in  which  we  may  lose  more  in  one  direc- 
tion than  we  gain  towards  the  end  we  are  trying  to  attain. 
To  use  the  air  expansively  it  must  be  admitted  to  the 
ejector  at  a  higher  pressure  than  is  required  to  over- 
come the  actual  head  plus  friction.  To  do  this  more 


184     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

work  is  required  from  the  compressor  at  the  power 
house.  Either  some  form  of  cut-off  valve  or  com- 
pensating device  must  be  employed  for  the  storage  of 
the  excess  power.  But,  like  the  direct -acting  simple 
pump,  a  certain  pressure  must  be  maintained  through- 
out the  stroke  or  discharge. 

In  the  case  of  the  ejector,  if  the  pressure  falls  below 
that  figure  it  will  not  empty,  the  weight  will  not  fall, 
and  the  exhaust  will  not  open.  Neither  will  the  ejector 
refill  as  the  exhaust  cannot  escape.  Unless  we  have  a 
higher  initial  pressure  it  is  difficult  to  see  how  expansive 
working  can  be  carried  out,  but  if  we  have  this  higher 
pressure  beyond  that  actually  required  to  raise  the 
effluent,  there  is  at  once  the  additional  loss  in  com- 
pression and  leakage  from  the  air  mains.  It  is  true  that 
when  ejectors  discharge  through  long  mains  the  last 
25  per  cent,  of  the  discharge  is  assisted  by  the  kinetic 
energy  of  the  liquid,  but  to  utilise  this  for  expansive 
working  of  the  air  would  need  precise  calculations  and 
a  uniform  pressure  for  each  discharge. 

A  smaller  volume  of  high-pressure  air,  admitted  to 
the  ejector  and  cut-off,  will,  no  doubt,  do  the  work  by 
expanding,  provided  there  is  no  leakage  whatever 
from  the  exhaust,  and  the  pressure  in  the  ejector  does 
not  fall  below  that  figure  required  to  overcome  the  total 
head  on  the  rising  main.  However,  in  dealing  with 
low  pressure  a  cut-off  valve  must  be  extremely  accurate 
and  air-tight  to  effect  such  a  purpose. 

The  pneumatic  control  of  the  ejector  is  simple,  effi- 
cient, and  reliable,  as  it  consists  of  piston  valves  which 
are  required  to  take  up  one  or  two  positions  only  irrespec- 
tive of  pressure  and  cut-off,  and  they  are  firmly  held  in 
position  by  air  pressure.  Moderate  leakage  does  not 
affect  their  working,  but  in  a  cut-off  valve  that  is  to 


IMPROVEMENTS  185 

admit  a  certain  volume  only,  any  leakage  from  that 
said  volume  and  the  air  will  fail  to  displace  the  liquid. 
Again,  the  air  pressure  in  the  main  must  not  vary  as  the 
volume  of  air  admitted  would  vary. 

In  certain  respects  there  is  no  secondary  power  or 
motive  fluid  so  easy  to  control  or  reliable  in  operation, 
but  it  is  extremely  sensitive  to  any  leakage,  and  easily 
loses  its  power.  The  merits  of  compressed  air  as  a  fluid 
power  must  be  mastered,  and  its  limits  carefully  borne 
in  mind  when  it  is  used  for  actuating  mechanical  devices. 

THE  Loss  FROM  Am  MAINS. 

Reason  No.  4.  The  loss  by  leakage  from  the  air  mains 
is  in  the  opinion  of  many  engineers  one  of  the  greatest 
objections  to  the  ejector  system.  A  great  deal  depends 
on  how  the  air  mains  are  laid,  in  the  first  place.  With 
efficient  supervision  the  leakage  will  be  small  in  after 
years.  To  reduce  the  expenses  from  air-main  loss  there 
are  three  ways : 

1.  Recaulking  the  pipes. 

2.  Doing  away  with  the  pipes. 

3.  Selling  the  air  for  other  purposes. 

Recaulking  the  joints  and  keeping  the  valves  in  a  good 
state  of  repair  is  an  elementary  but  none  the  less  most 
efficient  remedy.  In  ejector  systems  there  is  a  certain 
point  beyond  which  it  would  not  pay  to  go.  With  air  at 
only  20  and  30  Ibs.  the  square  inch,  it  is  quite  feasible  to 
keep  within  a  5  per  cent,  leakage  ;  but  whether  it  would 
cost  more  in  repairs  than  the  value  of  the  air  lost  much 
below  this  figure  is  open  to  question.  If  the  pipes  have 
been  well  laid,  joints  well  run,  and  no  short  lengths  per- 
mitted, it  is  a  simple  matter  as  no  re -running  is  required 
and  the  position  of  each  joint  can  be  marked  off  from 


186     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

the  surface.  On  the  other  hand,  if  careless  work  has 
been  the  practice  during  construction,  pipe  spigots, 
butted  against  pipe  sockets  with  no  room  for  running 
lead,  and  indiscriminate  laying  of  short  lengths  of  pipe, 
the  joints  cannot  be  located,  and  yards  of  pipe  will  have 
to  be  relaid  to  recaulk  a  single  joint  in  a  satisfactory 
manner. 

It  is  not  only  the  pipe  joints  but  the  stop  valves  that 
must  be  tight,  or  testing  lengths  of  pipe  to  locate  leakage 
cannot  be  carried  out.  It  is  possible  to  put  down  cast- 
iron  flanged  pipes  or  steel  pipes  with  flanges  suitably 
attached,  if  the  additional  capital  expense  is  not  ob- 
jected to.  In  busy  streets,  where  traffic  is  very  heavy 
and  it  is  worth  while  avoiding  the  inconvenience  of  a 
single  recaulking  after  the  pipe  has  once  been  put  down, 
the  extra  cost  may  be  justified,  but  it  must  be  remem- 
bered in  many  soils  the  life  of  the  steel  pipe  may  be  a 
disappointment. 

The  ordinary  cast-iron  spigot  and  socket  pipe  has 
great  merits  for  street  work.  It  is  easy  to  cut  to  any 
desired  length,  bends  can  be  placed  just  where  they  are 
wanted,  and  the  flexibility  of  the  joints  permits  of  con- 
siderable deviation  from  the  straight  line  which  it  is 
often  impossible  to  keep  to  owing  to  existing  water 
pipes,  valve  chambers,  and  many  other  such  obstruc- 
tions. It  is  the  cheapest  to  put  down,  simplest  to  joint, 
the  most  adaptable  to  varying  conditions,  and  easily 
repaired.  With  reasonable  care  and  a  very  moderate 
outlay  on  maintenance,  the  loss  to  an  ejector  system 
from  this  cause  can  be  kept  down  to  a  small  figure .  The 
loss  by  leakage  from  the  air  main  is  the  simplest  to  remedy, 
but  in  many  cases  it  is  permitted  to  be  the  greatest, 
even  running  up  to  20  per  cent,  and  30  per  cent.  The 
greater  the  volume  of  air  transmitted  by  the  mains  the 


IMPROVEMENTS  187 

less  is  the  proportional  loss  by  leakage,  and  the  less  is 
the  upkeep  per  1000  cubic  feet  of  air  compressed. 

It  must  not  be  supposed  from  these  remarks  that  cast- 
iron  spigot  and  socket  pipes  constantly  want  repair- 
ing ;  on  the  contrary,  when  the  joints  are  well  run,  well 
caulked,  and  the  pipes  well  bedded,  there  is  practically 
no  limit  to  the  time  they  will  remain  air-tight. 

For  an  ejector  system  laid  out  under  the  average  con- 
ditions, it  is  doubtful  if  there  is  any  improvement  to 
be  made  in  the  means  of  transmission  over  the  spigot 
and  socket  pipe  for  the  same  expenditure. 

ELECTRIC  TRANSMISSION. 

Suggestions  are  not  infrequently  made  that  the  air 
mains  should  be  done  away  with  in  order  to  avoid  leakage. 
No  doubt  this  would  be  a  most  effective  method  ;  but 
it  is  a  question  whether  the  remedy  may  not  be  more 
inefficient  than  the  evil.  It  has  been  proposed,  if  not 
actually  given  a  trial,  to  have  a  multiple  ejector  system 
with  a  central  power  station  for  the  generation  of  elec- 
tricity, which  is  transmitted  to  the  ejector  station  by 
cables  for  the  purpose  of  supplying  motors  for  driving 
small  air  compressors  at  each  of  the  ejector  stations. 
To  introduce  a  third  power  of  a  necessity  adds  further 
complications  and  losses  in  other  directions. 

Whether  we  use  internal-combustion  engines  or  steam 
engines,  it  is  the  first  essential  to  economy  to  generate 
power  in  bulk,  and  every  time  we  convert  one  power 
into  another  there  is  a  certain  amount  of  loss.  The 
smaller  the  power  unit,  the  greater  the  loss  from  friction 
and  less  the  efficiency.  If  we  have  a  multiple  ejector 
system  of  fifty  stations,  it  is  not  only  a  question  of  how 
much  we  should  lose  from  friction  and  inefficiency,  com- 
pared;to  the  loss  from  the  air  main,  but  the  additional 


188     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

risk  from  failure  by  the  introduction  of  further  mechanical 
motion  between  the  secondary  power  and  the  work  to 
be  done.  It  means  the  addition  of  two  motive  power 
engines  between  the  prime  power  and  the  work  it  has 
to  do.  Between  electric  cables  and  cast-iron  pipes  the 
difference  in  cost  is  not  great,  so  the  motor  and  com- 
pressor would  be  extra  cost  without  compensation,  and 
there  is  no  reason  to  suppose  that  the  mechanical  effi- 
ciency of  fifty  small  air  compressors  could  even  approach 
that  of  a  single  large  unit.  Again,  in  order  to  cope  with 
the  maximum  discharge  from  the  ejector,  the  compress- 
ing unit  would  either  have  to  be  in  duplicate  or  of  large 
size,  and  such  units  would  give  poor  results  under  normal 
conditions  existing  ninety-nine  days  out  of  a  hundred. 
That  more  supervision  would  be  required  is  a  certainty, 
and  the  repairs  to  an  ejector  station  which  now  amount 
to  'shillings  a  year  '  would  be  multiplied  a  hundredfold. 
Presumably  the  compressors  would  be  water  cooled,  and 
a  water  supply  would  be  required  for  each  station. 

Other  items  of  expense  could  also  be  enumerated,  but 
there  is  no  object  in  pursuing  this  method  further,  to 
show  that  the  initial  cost,  maintenance,  and  efficiency 
would  be  no  improvement  over  a  single  power  station 
for  compressing  the  air  in  bulk  and  distributing  it  to 
the  ejector  stations  by  means  of  cast-iron  spigot  and 
socket  pipes. 

SELLING  COMPRESSED  AIR. 

The  idea  of  reducing  the  loss  (expense)  by  leakage 
from  the  air  mains  by  *  selling  the  air '  may  seem  at 
first  '  far  fetched/  but  this  is  by  no  means  the  case. 
If  only  a  proportion  of  the  air  is  sold  it  will  assist  to 
make  a  compressed-air  system  self-supporting  in  place 
of  an  unremunerative  burden  on  the  ratepayers.  Care 


IMPROVEMENTS  189 

would  be  substituted  for  neglect,  as  it  is  now  only  too 
often  not  considered  worth  the  expense  to  maintain  air 
mains  in  a  high  state  of  efficiency.  Money  spent  on 
maintenance  would  be  money  saved  on  the  system,  in  a 
sense  which  is  not  now  realised.  The  greater  the  out- 
put of  air  the  greater  the  efficiency  of  boilers,  engine,  and 
compressors.  If  the  power  station  is  converted  from  a 
dead  loss  into  a  self-supporting  scheme,  the  whole  aspect 
of  a  compressed -air  drainage  system  changes.  Even  if 
the  rate  charged  for  the  air  was  only  sufficient  to  meet 
the  actual  expense  of  that  volume  sold,  the  air  that  is 
not  sold  but  used  by  the  ejectors  is  produced  at  a  cheaper 
rate  as  the  total  volume  compressed  is  greater,  the  pro- 
portional leakage  is  less,  and  it  would  be  worth  while  to 
reduce  that  leakage  to  a  minimum. 

USES  OF  COMPRESSED  Am. 

Compressed  air  at  low  pressure,  20  to  40  Ibs.,  is  an 
absurdly  cheap  power  when  generated  in  bulk  and 
distributed  as  a  secondary  power  ;  it  is  absolutely  safe 
and  easy  to  handle,  and  in  some  cities  it  can  be  used 
extensively  as  the  atomising  agent  for  burning  liquid 
fuel,  especially  for  domestic  purposes  and  firing  the 
kitchen  range.  Air  hoists,  pneumatic  despatch,  and 
raising  water  to  the  top  of  high  buildings  are  also  pur- 
poses for  which  it  possesses  exceptional  merits.  Inci- 
dentally, it  may  be  remarked  the  war  has  been  respon- 
sible for  the  use  of  compressed  air  for  culinary  purposes. 

COMPRESSED  AIR  FOR  DOMESTIC  OIL  FIRING. 

Cheap  firing  is  a  necessity  to  civilisation,  but  in  many 
Eastern  cities  the  price  of  coal  has  increased  so  enor- 
mously as  to  make  it  more  economical  to  burn  fuel  oil, 


190     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

but  it  cannot  be  used  economically  and  efficaciously  in  the 
kitchen  range  without  a  small  volume  of  compressed 
air  for  atomising  purposes.  In  coal-producing  countries 
it  is  not  likely  that  oil  will  be  extensively  used  as  a 
substitute  ;  but  there  are  many  cities  in  the  East,  such 
as  Cairo,  Bombay,  and  Rangoon,  where  compressed- 
air  systems  already  exist.  Indeed  the  compressed- 
air  Cairo  main  drainage  system  has  been  successfully 
used  for  firing  kitchen  ranges  for  the  last  twelve  months. 
The  average  pressure  in  use  for  ejector  systems  is  very 
suitable — that  is,  between  20  Ibs.  and  30  Ibs.  the  square 
inch — as  this  is  sufficient  for  atomising  the  heaviest  fuel 
oils  (residues),  which  are  the  cheapest. 

The  combustion  of  fuel  oil  in  the  kitchen  range  by 
means  of  compressed  air  shows  a  saving  of  50  per  cent, 
over  coal,  weight  for  weight,  and  in  all  cities  where  fuel 
oil  can  be  obtained  at  not  more  than  double  the  price 
of  coal  there  is  little  doubt  there  is  an  extensive  field 
for  its  use  in  combination  with  a  pneumatic -ejector 
system  for  draining  the  city. 

As  pointed  out  in  preceding  chapters,  the  commercial 
efficiency  of  a  compressed-air  system  for  draining  level 
districts  is  by  no  means  inferior  to  that  of  pumps,  and 
it  possesses  many  exclusive  merits,  which  engineers 
readily  admit,  but  the  cost  of  the  power  house  and  main- 
tenance has  made  many  authorities  hesitate  to  adopt 
it.  If,  however,  a  percentage  of  the  air  can  be  sold 
and  the  output  of  the  power  house  increased,  the 
costs  are  at  once  reduced,  even  if  the  sale  of  the  air  is 
not  on  such  a  large  scale  as  to  make  the  system  self- 
supporting. 

Though  hand  power  will  light  a  liquid-fuel  burner  for 
the  kitchen  range,  as  the  volume  of  air  required  is  so 
small,  it  cannot  compete  in  cost  with  the  generation  of 


IMPROVEMENTS  191 

power  in  bulk,  and  the  greater  the  volume  the  cheaper 
the  air. 

There  is  no  reason  why  compressed  air  should  not  be 
supplied  to  city  populations  for  combustion  purposes  in 
the  kitchen  range  in  the  same  way  as  water,  gas,  or 
electric  light.  If  it  pays  a  man  to  light  his  house  from 
a  power  station,  how  much  more  will  it  pay  him  to  cook 
his  dinner  when  the  power  costs  but  a  fraction  of  that 
from  which  he  derives  his  light. 

There  was  a  time  when  laying  a  gas  pipe  to  the  smallest 
rent  payer  in  a  city,  for  the  purpose  of  providing  light, 
was  ridiculed,  and  it  is  not  so  long  ago  that  electric  light 
was  regarded  as  a  luxury  for  the  rich  and  an  advert- 
isement for  up-to-date  theatres. 

But  the  novelty  of  to-day  is  the  accepted  necessity 
of  to-morrow,  and  these  means  of  illumination  are  as 
much  a  part  of  our  daily  lives  as  the  electric  tram  and 
motor  bus  of  every  large  city. 

COST  OF  COMPRESSING  AIR. 

As  previously  remarked,  compressed  air  is  an  absurdly 
cheap  secondary  power  at  low  pressure,  and  a  few  remarks 
concerning  the  cost  will  be  of  interest,  together  with 
how  much  air  such  burners  consume,  as  if  these  pages 
should  meet  the  eye  of  municipal  engineers  with  com- 
pressed-air systems  under  their  supervision  they  will 
be  able  to  form  some  idea  of  how  much  their  main- 
tenance costs  would  be  reduced  by  the  sale  of  the  air. 

The  fuel  cost  of  compressing  air  to  100  Ibs.  the  square 
inch  with  Diesel  oil  engines  is  claimed  to  be  as  low  as  1  Jd. 
per  1000  cub.  ft.  of  free  air.  This  may  be  exceptional, 
but  it  is  obvious  that  with  a  pressure  of  only  30  Ibs. 
the  square  inch,  Id.  per  1000  cub.  ft.  will  cover  the  cost 
under  the  same  conditions. 


192     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

However,  it  is  better  to  base  calculations  on  actual 
records,  poor  though  they  may  be,  than  on  possible 
performances,  and  the  figures  now  given  are  of  excep- 
tional interest. 

The  Cairo  compressed-air  system  is  a  large  one,  com- 
prising four  sets  of  triple  expansion,  steam,  air-compress- 
ing engines,  and  each  engine  is  capable  of  compressing 
2,000,000  cub.  ft.  of  free  air  per  day  of  twenty -four  hours 
at  a  pressure  of  22  Ibs.  the  square  inch,  which  gives  a  work- 
ing pressure  of  20  Ibs.  the  square  inch  in  distant  localities. 

For  the  year  1916-1917  the  volume  of  free  air  com- 
pressed was  573,240,000  cub.  ft.  at  a  total  maintenance 
cost,  including  fuel,  of  £E. 6878* 900,  which  equals  a  cost 
of  3d.  per  1000  cub.  ft.  of  free  air  compressed.  It  must 
be  understood  that  this  is  anything  but  economical,  but 
for  our  purpose  it  is  sufficient. 

In  the  present  state  of  the  sewage  scheme  there  is 
ample  reserve  power,  but  in  cases  where  there  is  not, 
an  extra  compressor  can  be  put  down,  and  by  slightly 
raising  the  pressure  when  abnormal  conditions  arise 
existing  mains  will  prove  of  sufficient  capacity. 

CONSUMPTION  OF  Am  FOR  LIQUID-FUEL  BURNERS. 

The  consumption  of  air  by  a  kitchen-range  burner  varies 
from  0'119  to  0'50  cub.  ft.  free  air  per  minute,  accord- 
ing to  the  size  of  the  range  and  extent  of  the  cooking. 
Taking  an  average  figure  of  0*30  cub.  ft.  per  minute,  this 
equals  18  cub.  ft.  per  hour,  or  216  cub.  ft.  per  day  of  twelve 
hours  or  78,840  cub.  ft.  per  year,  at  a  cost  of  just  under 
£E.1*000  (one  pound).  Allowing  for  leakage,  deprecia- 
tion, sinking  fund,  and  interest,  together  with  super- 
vision of  reticulation,  a  charge  of  £E.2'000  per  year  per 
burner  should  leave  a  good  profit.  Now  2,000,000  cub. 
ft.  of  free  air  at  20  Ibs.  pressure  will  supply  9259  domestic 


IMPROVEMENTS  193 

fuel  burners,  which  at  a  charge  of  £E.2*000  per  year  each 
would  produce  a  sum  of  £E.18,518'000. 

The  figures  given  are  Egyptian  pounds,  which  are 
worth  6d.  more  than  the  English  pound ;  this  makes  no 
difference  for  the  purpose  of  an  estimate,  and  it  is  easy 
to  see  that  a  sum  of  £18,500  will  go  a  long  way  to  make 
a  power  station  self-supporting  that  is  supplying,  say, 
2,000,000  cub.  ft.  of  air  a  day  for  drainage  and  2,000,000 
cub.  ft.  a  day  for  remunerative  purposes.  •  v 

All  large  consumers  would  be  charged  by  air  meter, 
and  precautions  taken  that  no  householder  should  be 
able  to  obtain  more  than  his  share. 

Ordinary  lead  piping,  such  as  used  for  water  and  gas, 
is  quite  suitable  for  laying  the  air  on  to  the  houses  and, 
being  jointless,  no  leakage  need  be  feared. 

COST  OF  OIL  FIRING  WITH  COMPRESSED  AIR. 

From  the  consumer's  point  of  view  there  is  no  question 
that  the  supplying  of  compressed  air  from  a  central 
power  house  is  by  far  the  cheapest  and  most  reliable, 
and  in  oil-producing  or  oil-burning  cities  it  is  the  means 
of  placing  cheap  firing  at  his  disposal.  Previous  to  the 
war  £2,  10s.  per  ton  for  fuel  oil  was  not  unusual,  and 
much  less  in  some  Eastern  towns.  Experience  shows 
that  the  domestic  range  consumes  from  2  Ibs.  to  9  Ibs. 
of  oil  per  hour,  according  to  the  size  of  the  range  and 
amount  of  cooking. 

In  the  average  household  4J  Ibs.  of  oil  per  hour  would 
probably  be  sufficient  for  seven  hours  a  day.  This 
equals  31  Ibs.  approx.  of  oil  per  day  at  a  yearly  cost 
of  about  £12,  10s.  or,  plus  the  compressed  air,  £14,  10s. 
To  compete  with  this  figure  coal  must  not  exceed  27s. 
per  ton. 

The  supervision  of  a  300  horse-power  plant  costs  as 

N 


194    EFFICIENCY  OF  PUMPS  AND  EJECTORS 

much  as  the  supervision  of  a  600  horse -power  plant,  and 
the  cost  of  the  fuel  diminishes  in  proportion  with  the 
greater  power.  In  an  air-main  system,  when  all  the 
mains  are  in  use,  the  loss  by  leakage  is  precisely  the  same 
whether  8000  cub.  ft.  or  8,000,000  cub.  ft.  of  air  are 
being  used  per  day  ;  but  the  smaller  the  volume  used 
the  greater  the  proportional  loss,  and  the  greater  the 
volume  used  the  less  the  proportional  loss.  Therefore 
the  greater  the  consumption  of  air  the  higher  is  the 
efficiency  of  the  installation. 

If  the  compressed  air  from  a  pneumatic  ejector  power 
house  can  be  sold  for  domestic  and  industrial  purposes, 
we  are  much  more  likely  to  increase  the  efficiency  of  the 
system  by  making  full  use  of  the  air  mains  than  by 
doing  away  with  them.  That  there  are  improvements 
to  be  carried  out  in  the  use  of  compressed  air  which  will 
increase  the  efficiency  of  the  system,  there  can  be  little 
doubt. 

Am  STORAGE. 

Reasons  5  and  6.  The  great  variation  in  the  volume 
of  air  required  in  the  twenty-four  hours  is  a  cause  of 
inefficiency. 

To  store  the  air  would  appear  to  be  the  obvious  remedy, 
but  at  the  low  pressure  used  this  would  need  receivers 
of  impossible  dimensions.  To  store  the  air  there  is  little 
doubt  the  pressure  would  have  to  be  raised  considerably, 
and  to  raise  the  pressure  we  should  at  once  decrease  the 
efficiency  of  the  air  compressor.  In  small  schemes 
comprising  two  or  three  small  ejector  stations,  storage 
is  quite  feasible  for  one  or  two  hours,  but  as  soon  as  we 
come  to  large  powers  there  is  little  doubt  it  is  more 
satisfactory  and  economical  to  keep  the  engine  running. 


IMPROVEMENTS  195 

In  large  plants  many  other  factors  besides  the  com- 
pressed air  have  to  be  taken  into  account  in  stopping 
and  starting  up  the  machinery.  In  most  cities,  especially 
dry  countries,  the  flow  of  sewage  is  regular,  but  the 
variation  is  great,  according  to  the  hour  of  the  day. 
From  1  A.M.  to  4  A.M.  the  flow  will  be  at  its  minimum, 
whereas  from  7  A.M.  to  12  P.M.  three  or  four  times  as 
much  power  may  have  to  be  provided  for.  The  flow  is 
gradually  rising  or  gradually  falling  at  most  hours  of 
the  twenty -four.  It  is  from  this  fact,  more  than  all 
else,  that  makes  it  so  difficult  to  obtain  the  economy 
one  would  expect  by  installing  internal-combustion 
engines  in  place  of  steam  engines.  By  careful  regula- 
tion, a  steam  engine  that  will  give  the  maximum  daily 
output  required  can  be  run  dead  slow  to  suit  the  minimum 
flow ;  but  with  the  internal-combustion  engine  a 
certain  speed  is  essential,  and  the  surplus  air  has  to  be 
blown  to  waste  or  some  automatic  device  provided 
for  cutting  out  the  compressors  while  the  engine  is 
running. 

This  reason  of  inefficiency  is  inherent  to  the  ejector 
system.  It  could  be  done  away  with  by  storing  the 
sewage,  but  to  do  this  we  should  at  once  destroy  one 
of  the  outstanding  merits  of  the  ejector.  Automatic 
regulation  from  the  air  pressure  has  so  far  not  proved 
very  successful,  and  as  the  real  fault  is  the  direct  result 
of  performing  the  work  to  be  done  in  an  efficient  manner, 
from  another  point  of  view,  other  than  mechanical,  it 
is  a  case  of  one  efficiency  having  to  give  way  to  another. 
Such  being  the  case,  the  most  effective  improve- 
ment is  the  extension  of  the  use  of  compressed  air, 
as  the  larger  the  volume  required  the  less  would  be 
the  loss. 


196     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

REASONS  OF  FLUCTUATION  IN  AIR  PRESSURE  :  REMEDIES. 

Reasons  7  and  8  may  be  taken  together.  There  is 
probably  no  class  of  power  system  in  which  there  is 
such  an  absence  of  uniform  running  conditions  and  con- 
stant fluctuation  in  pressure,  especially  compared  to  a 
pumping  plant. 

As  the  volume  of  air  required  is  always  rising  or  falling, 
the  driver  must  be  constantly  adjusting  his  engines,  and 
the  fireman  attending  to  the  dampers,  furnace,  and  feed 
water  of  his  boiler.  He  should,  of  course,  anticipate 
the  demands  to  be  made  on  the  boiler,  but  this  is  exactly 
what  he  is  not  able  to  do.  The  first  intimation  the  fire- 
man receives  of  a  demand  for  more  steam  is  a  falling 
gauge,  as  the  driver  in  the  engine  house  has  opened  the 
steam  valve  to  increase  the  speed  of  the  engine,  to  make 
good  a  falling  air  pressure.  Possibly  it  is  opened  a  shade 
in  excess  of  what  is  required  or  not  enough.  The  fire- 
man has  no  idea  if  he  will  have  further  demands  on  the 
boiler  in  the  next  five  minutes,  or  whether  it  will  be 
blowing  off  steam.  If  he  is  pressed  for  steam  he  prob- 
ably reduces  the  feed  and  brings  the  water  down  an 
inch  or  so  in  the  glass,  then  when  he  eventually  fills 
up  again  there  is  a  further  fluctuation  in  pressure,  and 
it  is  a  rare  thing  to  get  more  than  a  few  hours'  steady 
run  in  the  twenty -four.  It  must  be  remembered  the 
fluctuations  in  running  a  boiler  are  just  as  detrimental 
to  efficiency  as  fluctuations  in  the  engine,  and  their  steadi- 
ness depends  on  the  uniform  conditions  of  the  work  to 
be  done. 

Compressed  air  is  similar  to  a  spring  under  tension, 
and  if  we  can  imagine  a  pressure  at  one  end  of  the  spring 
and  a  variable  resistance  at  the  other,  it  is  easy  to 
understand  that  as  the  resistance  alters  so  must 


, 
IMPROVEMENTS  197 

the  pressure,  if  the  spring  is  to  be  kept  at  the  same 
tension. 

Similar  conditions  are  not  unknown  in  mechanical 
practice,  and  an  equilibrium  between  the  power  and 
the  work  is  usually  maintained  by  an  accumulator,  in 
which  surplus  energy  is  stored,  thus  permitting  a  uniform 
speed  of  the  engine  compressing  the  air. 

To  improve  the  efficiency  of  an  ejector  system  by  such 
means  we  should  require  an  apparatus  on  the  same 
lines.  Air  receivers  of  considerable  capacity  are  already 
part  of  the  plant,  and  there  seems  to  be  no  reason  why 
an  overhead  water  reservoir  at  a  suitable  height  to 
correspond  with  the  required  head,  and  of  a  capacity 
to  suit  the  receivers,  should  not  be  provided,  and  the 
necessary  connections  arranged.  This  would  have  the 
effect  of  steadying  the  pressure  against  which  the  engine 
is  running.  It  would  fulfil  the  same  purpose  as  that 
of  a  stand  pipe  on  a  pumping  installation. 

Assuming  the  engine  is  running  at  100  revolutions  per 
minute  at  a  steady  pressure  of  22  Ibs.  the  square  inch, 
this  is  what  occurs  :  a  sudden  demand  for  air  above  the 
normal  is  made  at  one  of  the  large  ejector  stations. 
Instead  of  the  pressure  falling,  the  water  from  the  over- 
head reservoir  runs  into  the  air  receivers  and  displaces 
a  volume  of  air  in  addition  to  the  constant  flow  from  the 
engines.  The  driver  will  see  from  the  level  of  the  water 
if  the  demand  is  temporary  or  continuous.  If  necessary 
he  increases  the  speed  of  his  engine  and  the  volume  of 
water  that  has  displaced  the  air  is  forced  back  into  the 
reservoir  when  the  demand  is  again  normal,  or  if  the 
demand  for  extra  air  soon  ceases  there  may  be  no  altera- 
tion of  the  speed,  the  normal  discharge  of  air  being 
sufficient  to  keep  the  water  out  of  the  air  receiver. 

By  this  means  it  is  possible  to  run  the  boilers  and 


198     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

engines  against  a  constant  pressure  ;  the  efficiency  would 
be  improved,  as  the  running  conditions  would  be  more 
uniform. 

When  engines  are  running  under  normal  conditions 
at  almost,  if  not  quite,  their  maximum  speed,  there  is 
very  little  doubt  considerable  saving  by  such  means 
would  be  effected,  as  it  is  on  such  occasions  that  the 
pressure  cannot  be  prevented  from  falling,  and  there 
is  always  some  hesitation  as  to  whether  it  is  worth  while 
starting  up  reserve  engines  to  recover  a  pound  pressure. 

IMPROVEMENTS  DEFINED. 

This  chapter  is  headed  '  improvements.'  Few  realise 
the  true  meaning  of  this  word,  and  fewer  still  are  those 
who  are  able  to  initiate  and  carry  them  out.  The  mere 
substitution  of  one  power  for  another  does  not  come 
under  the  heading,  as  the  most  economical  type  of 
power  unit  is  invariably  decided  by  local  conditions. 
A  real  improvement  is  actually  saving  or  re -using  a  per- 
centage of  the  power  generated,  without  the  additional 
expenditure  on  maintenance  being  of  such  magnitude, 
as  to  exceed  the  cost  of  the  power  saved,  or  again  the 
improvement  of  some  mechanical  detail  which  saves 
power,  labour,  and  expense. 

To  accomplish  this  requires  long  experience  and  an 
exhaustive  study  of  the  power  and  the  work  it  is  doing, 
together  with  resource,  self-reliance,  and  wisdom.  The 
generation  and  application  of  power  is  the  interpreta- 
tion of  physical  science. 

All  science  starts  from  a  common  basis — that  is,  fact 
and  reason — and  there  is  nothing  more  remarkable  how 
true  thinkers,  and  those  who  have  mastered  their  pro- 
fession, in  theory  and  practice,  proceed  on  the  same  lines 
of  thought  to  solve  original  problems  that  tend  to 


IMPROVEMENTS  199 

improve  efficiency  and  utilise  the  means  at  our  disposal 
to  the  best  advantage. 

The  nature  of  the  problem  is  of  little  consequence,  as 
there  is  a  sympathy  of  mind  and  method  which  is  entirely 
absent  to  the  superficial  intellect.  We  must  strive  for 
perfection  in  practice  and  utilise  experience,  besides 
possessing  scientific  ability,  as  the  one  without  the 
other  is  a  superficial  knowledge  of  the  subject  whatever 
it  may  be. 

Practice  unassisted  by  science  is  crude  and  clumsy, 
restricted  to  narrow  limits  and  elementary  tasks,  but 
theoretical  science  alone  is  a  negligible  quantity,  as  we 
cannot  use  an  abstract  faculty  independent  of  action. 
A  superficial  knowledge  of  physiological,  theoretical, 
and  material  things  is  the  baneful  curse  of  daily  prac- 
tice. To  master  a  power  problem,  the  driving  force, 
the  bed-rock  on  which  it  is  founded,  must  be  analysed 
and  examined,  and  the  why  and  wherefore  of  actual 
facts  of  scientific  laws  ineffably  impressed  upon  the 
mind  from  daily  experience. 

It  is  the  secret  of  resource  and  self-reliance. 

It  is  better  by  far  to  excel  in  one  direction  than  to 
be  content  with  superficial  attainments,  for  the  simple 
reason  the  power  to  excel  in  one  direction  gives  us  the 
power  to  excel  in  others.  Every  engineer,  every  indi- 
vidual possesses  some  gift  or  latent  ability  that  is  capable 
of  being  more  highly  developed  than  others.  Foster  it, 
encourage  it.  It  is  in  the  application  of  such  gifts  that 
he  will  benefit  the  profession  and  rise  out  of  the  con- 
ventional rut  of  repetition  work. 

Practise  that  particular  bent  in  which  the  inclination 
leads.  Absorb  every  atom  of  knowledge  on  that  par- 
ticular subject  that  comes  within  reach.  The  mind  will 
eagerly  do  so,  and  you  are  ready  to  advance  from  that 


200     EFFICIENCY  OF  PUMPS  AND  EJECTORS 

point  of  supposed  perfection  where  others  have  left  off. 
A  superficial  knowledge  of  a  hundred  different  things  is 
a  poor  substitute  for  wisdom  in  a  single  sphere,  as  wisdom 
is  the  power  of  applying  knowledge,  the  ability  to  put 
into  practice  what  we  have  learned  with  prudence  and 
discretion. 

To  carry  out  improvements  it  is  just  this  mastery  of 
thought  and  action  that  we  want  to  gain  before  all  else  ; 
no  matter  by  what  particular  road  we  gain  it,  there  is  no 
subject  that  will  not  yield  to  its  onslaught.  It  is  the 
master  key  that  will  open  many  doors,  and  more  precious 
than  all  the  academic  distinctions  that  any  man  can 
win. 

For  this  reason  science  is  truth,  and  great  truths  all 
start  from  the  same  basis  and  are  founded  on  the  same 
laws,  and  the  methods  of  thought  applied  in  one  case 
are  equally  applicable  in  others.  And  that  is  why  all 
true  thinkers  and  men  of  action  who  possess  wisdom 
have  views  in  common,  and  are  able  to  approach  a 
difficult  problem  in  such  a  way  that  it  is  most  easily 
solved.  They  seize  the  essentials,  and  half  the  battle 
is  won. 

There  are  no  difficulties  for  those  who  have  gained 
wisdom :  it  is  only  the  ignorant  who  create  them.  There 
is  no  weight  of  responsibility  on  the  experienced,  as  they 
know  how  to  adjust  the  heaviest  load. 

Intellectual  attainments  are  often  mistaken  for  wisdom. 
An  engineer  may  be  highly  educated  in  every  science, 
and  the  recipient  of  degrees  and  honours,  but  the  power 
of  vivid  reflection  or  preconception  from  the  analysis 
of  detail  and  synthetic  thought  is  the  only  basis  of  con- 
vincing logic  and  accurate  foresight  which  enables  us 
to  utilise  precedent  and  predict  the  consequences  of  our 
deductions.  Banish  from  the  mind  all  thought  of  in- 


IMPROVEMENTS  201 

spired  wisdom.  There  is  no  such  thing.  Some  minds 
will  work  faster  than  others,  and  some  subjects  are  less 
laborious  than  others,  but  the  more  laborious  the  subject 
the  greater  the  measure  of  the  reward.  As  truth  is  to 
false  conception,  so  is  wisdom  to  folly,  and  folly  is  the 
putting  into  practice  of  superficial  attainments. 


INDEX 


ACCESSORIES  to  power  house,  154, 

155. 
Air,  compressed,  latent  power,  176, 

177. 
,,  ,,          for  oil-firing,  189, 

191. 
,,  ,,          consumption       by 

burners,  192. 
„   coolers,  156. 
,,    cost  of  compressing,  191. 
,,   lock  on  rising  mains,  131. 
,r  lock  for  tubbings,  102. 
,,    mains  (see  mains). 
,,    pressure  fluctuations,  196,  198. 
,,    in  pumps,  11. 

,,    selling  compressed  air,  188, 189. 
,,    for  sinking  tubbings,  109. 
„    stop  valves,  127,  128. 
,,    storage  of  compressed  air,  194, 

195. 

,,    temperature  diagram,  157. 
,,    uses  of  compressed  air,  189. 
,,   vessels  on  pumps,  14. 
,,   volume     (diagrams)     to     raise 

sewage,  158-166. 
,,    waste  of  exhaust,  179-181. 

BOILERS,  oil-firing,  189-193. 

Brick   chambers  for  ejectors,   108, 

109. 
Burners  (oil),  consumption  of   air, 

192. 
Burners   (oil),  consumption  of   oil, 

172,  193. 

CALIBRATING,     the     discharge     of 

pumps  and  ejectors,  46-52. 
Centrifugal  pumps,  24,  26,  32,  33, 

36,  38. 
Chambers,  brick,  for  ejectors,  108, 

109. 

,,         screening,  67. 
,,         silencing,    for    exhaust, 

113. 

,,        for  stop  valves,  129. 
Chemical    test  of  Venturi    meter, 
52-53. 


Commercial  efficiencies,   1,  65,  84, 

85. 
Covers  for  tubbings,  117,  118. 

DANGERS  from  explosion  and  gas, 

38,  39. 
Discharge  of   pumps  and  ejectors, 

46-52,  75. 

,,          of  ejectors,  49. 
,,  ,,  and  Venturi 

meter,  52. 

EFFICIENCY  defined,  1. 

commercial,  1,  65,  84. 

„      tables,  84,  85. 
mechanical,  1,  43. 

table,  44. 

sanitary,  2,  133,  141. 
summary  of,  64. 
Electric  motors  for  pumps,  39. 
„     reliability,  40. 
,,        transmission,  187,  188. 
Engine  foundations,  150,  151. 
,,      house  floors,  152. 
,,      for  raising  sewage,  147-149. 
Ejectors,  action  on  sewage,  29-31. 
advantages,  34,   72,   142, 

145. 
,,          blow  through,  113. 

calibrating  discharge,  46- 

52. 

,,          capacity  of,  46. 
,,          causes  of  stopping,  112. 
choking  of,  114. 
compounding,  177,  178. 

,,  objections, 

181-182. 

cost  of  system,  73. 
description    of    working, 

27-29. 
discharge  diagrams,  159, 

162,  165. 
,,        table,  49, 
efficiency    diagrams,    56, 

58. 

„       trials,  56-62. 
erection,  106. 

203 


204    EFFICIENCY  OF  PUMPS  AND  EJECTORS 


Ejectors,   examination    of    valves, 
115,  116. 

,,          exhaust  air,  179-181. 

,,          exhaust    air,    recompres- 
sion,  182,  183. 

,,          exhaust  silencing   cham- 
ber, 113. 

,,          expansion  of  air  in,  183 
185. 

,,          false  discharges,  116. 
faults,  111-112. 

,,          floating   matter  in,    114, 
115. 

„          inefficiency  of,  174,  175. 

,,          inlet  pipes,  107. 

,,          inspection  of,  94. 

,,          maintenance    (see    main- 
tenance). 

,,          painting,  117. 

,,          sand  and  stones  in,  114. 

,,          silencing  chamber,  113. 

,,          slide-valve  leakage,  115. 

,,          stations,  71. 

,,          stopping  of,  116. 

,,          subsidiary,  27. 

,,          summary  of  installation, 
70. 

,,          trial  conditions,  56-62. 

,,          in  tubbings,  26. 

,,          working  of  system,  71-72. 

FLOORS  for  engine  house,  152. 
Fouling  of  sewage  mains,  131. 
Fuel  for  boiler  furnaces,  166. 

GAS-FIRING  for  boilers,  172-173. 
Gauges,  pressure,  53. 

,,  ,,       table  of  errors,  54. 

Grade  of  sewers,  143. 
Gravitation  sewers,  133. 
Ground  sections,  137-140. 

HYDRAULIC  system  of  raising  sew- 
age, 35. 

IMPROVEMENTS  denned,  198-201. 
,,  to  ejectors,  176. 

Indicator  plates,  132. 
Inefficiency  of  ejector  systems,  174, 

175. 
Inspection  openings  on  rising  mains, 

131. 
Inspectors'  (ejectors)  duties,  93. 

JOINTS,  pipe,  spigot  and  socket,  121- 

123. 
„      red  lead  in  ejectors,  107. 


LEAKAGE  from  air  mains,  54,  125, 

185. 
Localities  classified,  31,  32. 

MACHINERY  for  raising  sewage,  2. 
,,  foundations,  150,  151. 

,,  painting,  117. 

,,  suitable  conditions,  32- 

34. 

Mains,  accidents  to  air,  129. 
,,  ,,  sewage,  132. 

„      air,  71,  120. 
, ,      air  lock  in  rising  mains,  131. 
,,      back     pressure     in     rising 

mains,  130. 

„      caulking,  120,  123,  126. 
,,      detecting  leakage,  125,  126. 
,,      filling  trenches,  126. 
,,      fouling  of,  131. 

inspection  openings,  131. 
laying  of,  121-123. 
locating  stoppage,  131. 
losses,  54,  185,  186. 
rising,  68,  130. 
scour  valves  for,  132. 
steam,  152-154. 
testing  (table),  55. 
testing  when  laid,  55,  124. 
water  in,  126. 
Maintenance,  74. 

,,  ejector  tables,  80,  83. 

,,  pump  tables,  77-79. 

Meters,  Venturi,  51-53. 
Motors,  electric,  39-40. 

OIL-FIRING  for  boilers,  168-172. 
cost,  193-194. 
with     compressed     air, 
189,  191. 

PAINTING  machinery,  117. 
Pipes  (see  mains). 
Power  house,  147. 

accessories,  154,  155. 
auxiliaries,  67. 
design,  150. 
economy  in  running, 

166. 

engines,  147-149. 
floors,  152. 
ventilation,  152. 
water  supply,  155. 
Pumping  station  staff,  90. 

installation  cost,  73. 
Pumps,  advantages,  69,  143. 
air  and  gas  in,  11,  12. 
air  vessels  for,  14. 
analysis,  3. 


INDEX 


205 


Pumps,  calibrating  discharge,  46. 
centrifugal,  24,  26,  32,  33. 
efficiency  diagram,  44. 
foundations,  150,  151. 
matter  in,  12,  13. 
multiple  system,  36-38. 
reasons  of  preference,  143, 

144. 

reciprocating,  6-9,  33,  63. 
strainers,  13. 
suction,  10. 
summary  of  installation,  65, 

66. 

trials,  62,  63. 
working  of,  68. 


QUARTERS  for  staff,  93. 


RAMMERS,  126. 

Reciprocating  pumps,  6-9,  33,  63. 
Refuse  in  sewage,  41. 
Reports,  74. 

SAND  and  stones  in  ejectors,  114. 
Sanitary  efficiency,  2,  133,  141. 
Screening  chambers,  67. 
Sewage  (crude)  defined,  3. 
Sewerage   scheme   (example),    144- 

146. 

Sewers,  grade,  143. 
Silencers  for  exhaust,  113. 
Staff,  ejectors,  91,  92. 

inspectors'  duties,  93. 

pumping  station,  77,  78,  90, 
91. 

quarters,  93. 

selection  of,  94-99. 

supervising,  87. 
Steam  mains,  152. 
Stop  valves,  127. 
Strainers  for  suction,  13. 
Subsoil,  134-141. 
Sumps,  38,  39,  67. 
Systems,  sectional,  35,  142, 


TESTING  air  mains,  124. 

,,       ejector  chambers,  109. 
,,       pressure  gauges,  53. 
,,       Venturi  meter,  52. 
Trials  of  ejectors,  56-62. 
Trenches,  filling  and  ramming,  126. 
Tubbings,  100. 

,,         air  lock  for,  102. 

,,         air    valves,   position  in, 

119. 

,,         covers,  117,  118. 
,,        floors,  fixing,  105. 
,,         marking  out,  101. 
,,         obstructions  in  sinking, 

119,  120. 
,,         painting,  117. 

sinking,     101-104,     107- 

113. 
ventilation,  116,  117. 

USES  of  compressed  air,  189. 

VALVES,  air  stop,  127. 

automatic  ejector,  119. 

chambers,  129. 

disc,  120. 

ejector,  115,  116. 

foot,  13,  14. 

leather-hinged,  16. 

multiple-pump,  18-23. 

pump,  15. 

reflux,  118. 

slide-valve  leakage,  115. 

scour,  in  mains,  132. 
Ventilation  of  tubbings,  116,  117. 
,,  of  power  house,  152. 

Venturi  meter,  51-53. 

WATER,  behaviour  in  motion  and 

under  pressure,  4-6. 
, ,       in  air  mains,  126. 
,,       in  ejector  silencers,  113. 
,,       in  steam  mains,  152-154. 
,,       supply    for    power    house, 

155. 
Wells,  suction,  10. 


Printed  by  T.  and  A.  COKSTABLB,  Printers  to  His  Majesty 
at  the  Edinburgh  University  Press 


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